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C Programming Code Examples

C > Data Structures Code Examples

Basic binary search tree routines

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/* Basic binary search tree routines */ #include <stdio.h> #include <stdlib.h> struct tnode { int data; struct tnode *left; struct tnode *right; }; /* insert, swap, search value, search minimum and search maximum values */ struct tnode *tnode_insert(struct tnode *p, int value); struct tnode *tnode_swap(struct tnode *p); struct tnode *tnode_search(struct tnode *p, int key); struct tnode *tnode_searchmin(struct tnode *p); struct tnode *tnode_searchmax(struct tnode *p); /* destroy, count tree nodes */ void tnode_destroy(struct tnode *p); int tnode_count(struct tnode *p); /* print binary tree inorder, preorder, postorder [recursive] */ void print_inorder(struct tnode *p); void print_preorder(struct tnode *p); void print_postorder(struct tnode *p); int main(void) { int demo_nr[] = {1, 3, 4, 7, 2, 9, 9, 0, 5, 6, 8, 7, 1, 2, 4}; struct tnode *root = NULL; struct tnode *searchval = NULL; int querry = 0; int i = 0; /* demo: insert some nr's into the binary tree */ for(i = 0; i < 15; i++) root = tnode_insert(root, demo_nr[i]); printf("=-=-=\n"); printf("Total number of tree nodes: %d\n", tnode_count(root)); printf("inorder : "); print_inorder(root); printf("\n"); printf("preorder : "); print_preorder(root); printf("\n"); printf("postorder: "); print_postorder(root); printf("\n"); printf("=-=-=\n"); printf("Enter integer, find: "); scanf("%d", &querry); searchval = tnode_search(root, querry); if(searchval == NULL) printf(" * %d Not! found in btree\n", querry); else printf(" * Found! %d in btree\n", searchval->data); searchval = NULL; printf("Searching for Minimum value\n"); searchval = tnode_searchmin(root); if(searchval == NULL) printf(" * Minimum Not! found in btree ?\n"); else printf(" * Found! minimum value %d in btree\n", searchval->data); searchval = NULL; printf("Searching for Maximum value\n"); searchval = tnode_searchmax(root); if(searchval == NULL) printf(" * Maximum Not! found in btree ?\n"); else printf(" * Found! Maximum value %d in btree\n", searchval->data); printf("=-=-=\n"); printf("Exchanging all tree nodes: left <-> right\n"); root = tnode_swap(root); printf("inorder : "); print_inorder(root); printf("\n"); printf("preorder : "); print_preorder(root); printf("\n"); printf("postorder: "); print_postorder(root); printf("\n"); printf("=-=-=\n"); printf("Destroying btree... bye!\n"); tnode_destroy(root); return 0; } /* insert a tnode into the binary tree */ struct tnode *tnode_insert(struct tnode *p, int value) { struct tnode *tmp_one = NULL; struct tnode *tmp_two = NULL; if(p == NULL) { /* insert [new] tnode as root node */ p = (struct tnode *)malloc(sizeof(struct tnode)); p->data = value; p->left = p->right = NULL; } else { tmp_one = p; /* Traverse the tree to get a pointer to the specific tnode */ /* The child of this tnode will be the [new] tnode */ while(tmp_one != NULL) { tmp_two = tmp_one; if(tmp_one ->data > value) tmp_one = tmp_one->left; else tmp_one = tmp_one->right; } if(tmp_two->data > value) { /* insert [new] tnode as left child */ tmp_two->left = (struct tnode *)malloc(sizeof(struct tnode)); tmp_two = tmp_two->left; tmp_two->data = value; tmp_two->left = tmp_two->right = NULL; } else { /* insert [new] tnode as left child */ tmp_two->right = (struct tnode *)malloc(sizeof(struct tnode)); tmp_two = tmp_two->right; tmp_two->data = value; tmp_two->left = tmp_two->right = NULL; } } return(p); } /* print binary tree inorder */ void print_inorder(struct tnode *p) { if(p != NULL) { print_inorder(p->left); printf("%d ", p->data); print_inorder(p->right); } } /* print binary tree preorder */ void print_preorder(struct tnode *p) { if(p != NULL) { printf("%d ", p->data); print_preorder(p->left); print_preorder(p->right); } } /* print binary tree postorder */ void print_postorder(struct tnode *p) { if(p != NULL) { print_postorder(p->left); print_postorder(p->right); printf("%d ", p->data); } } /* returns the total number of tree nodes */ int tnode_count(struct tnode *p) { if(p == NULL) return 0; else { if(p->left == NULL && p->right == NULL) return 1; else return(1 + (tnode_count(p->left) + tnode_count(p->right))); } } /* exchange all left and right tnodes */ struct tnode *tnode_swap(struct tnode *p) { struct tnode *tmp_one = NULL; struct tnode *tmp_two = NULL; if(p != NULL) { tmp_one = tnode_swap(p->left); tmp_two = tnode_swap(p->right); p->right = tmp_one; p->left = tmp_two; } return(p); } /* locate a value in the btree */ struct tnode *tnode_search(struct tnode *p, int key) { struct tnode *temp; temp = p; while(temp != NULL) { if(temp->data == key) return temp; else if(temp->data > key) temp = temp->left; else temp = temp->right; } return NULL; } /* locate a minimum value in the btree */ struct tnode *tnode_searchmin(struct tnode *p) { if(p == NULL) return NULL; else if(p->left == NULL) return p; else return tnode_searchmin(p->left); } /* locate a maximum value in the btree */ struct tnode *tnode_searchmax(struct tnode *p) { if(p != NULL) while(p->right != NULL) p = p->right; return p; } /* destroy the binary tree */ void tnode_destroy(struct tnode *p) { if(p != NULL) { tnode_destroy(p->left); tnode_destroy(p->right); free(p); } }
malloc() Function in C
Allocate memory block. Allocates a block of size bytes of memory, returning a pointer to the beginning of the block. The content of the newly allocated block of memory is not initialized, remaining with indeterminate values. If size is zero, the return value depends on the particular library implementation (it may or may not be a null pointer), but the returned pointer shall not be dereferenced. The "malloc" or "memory allocation" method in C is used to dynamically allocate a single large block of memory with the specified size. It returns a pointer of type void which can be cast into a pointer of any form. It doesn't Iniatialize memory at execution time so that it has initializes each block with the default garbage value initially.
Syntax for malloc() Function in C
#include <stdlib.h> void* malloc (size_t size);
size
Size of the memory block, in bytes. size_t is an unsigned integral type. On success, function returns a pointer to the memory block allocated by the function. The type of this pointer is always void*, which can be cast to the desired type of data pointer in order to be dereferenceable. If the function failed to allocate the requested block of memory, a null pointer is returned.
Data races
Only the storage referenced by the returned pointer is modified. No other storage locations are accessed by the call. If the function reuses the same unit of storage released by a deallocation function (such as free or realloc), the functions are synchronized in such a way that the deallocation happens entirely before the next allocation.
Exceptions
No-throw guarantee: this function never throws exceptions.
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/* allocate memory block by malloc() function example */ // Program to calculate the sum of n numbers entered by the user #include <stdio.h> #include <stdlib.h> int main() { int n, i, *ptr, sum = 0; printf("Enter number of elements: "); scanf("%d", &n); ptr = (int*) malloc(n * sizeof(int)); // if memory cannot be allocated if(ptr == NULL) { printf("Error! memory not allocated."); exit(0); } printf("Enter elements: "); for(i = 0; i < n; ++i) { scanf("%d", ptr + i); sum += *(ptr + i); } printf("Sum = %d", sum); // deallocating the memory free(ptr); return 0; }
free() Function in C
The free() function in C library allows you to release or deallocate the memory blocks which are previously allocated by calloc(), malloc() or realloc() functions. It frees up the memory blocks and returns the memory to heap. It helps freeing the memory in your program which will be available for later use. In C, the memory for variables is automatically deallocated at compile time. For dynamic memory allocation in C, you have to deallocate the memory explicitly. If not done, you may encounter out of memory error.
Syntax for free() Function in C
#include<stdlib.h> void free(void *ptr).
ptr
This is the pointer to a memory block previously allocated with malloc, calloc or realloc to be deallocated. If a null pointer is passed as argument, no action occurs. This function does not return any value.
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/* deallocate memory block by free() function example */ #include <stdio.h> #include <stdlib.h> #include <string.h> int main () { char *str; /* Initial memory allocation */ str = (char *) malloc(15); strcpy(str, "HappyCodings"); printf("String = %s, Address = %u\n", str, str); /* Reallocating memory */ str = (char *) realloc(str, 25); strcat(str, ".com"); printf("String = %s, Address = %u\n", str, str); /* Deallocate allocated memory */ free(str); return(0); }
If Else If Ladder in C/C++
The if...else statement executes two different codes depending upon whether the test expression is true or false. Sometimes, a choice has to be made from more than 2 possibilities. The if...else ladder allows you to check between multiple test expressions and execute different statements. In C/C++ if-else-if ladder helps user decide from among multiple options. The C/C++ if statements are executed from the top down. As soon as one of the conditions controlling the if is true, the statement associated with that if is executed, and the rest of the C else-if ladder is bypassed. If none of the conditions is true, then the final else statement will be executed.
Syntax of if...else Ladder in C
if (Condition1) { Statement1; } else if(Condition2) { Statement2; } . . . else if(ConditionN) { StatementN; } else { Default_Statement; }
In the above syntax of if-else-if, if the Condition1 is TRUE then the Statement1 will be executed and control goes to next statement in the program following if-else-if ladder. If Condition1 is FALSE then Condition2 will be checked, if Condition2 is TRUE then Statement2 will be executed and control goes to next statement in the program following if-else-if ladder. Similarly, if Condition2 is FALSE then next condition will be checked and the process continues. If all the conditions in the if-else-if ladder are evaluated to FALSE, then Default_Statement will be executed.
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/* write a C program which demonstrate use of if-else-if ladder statement */ #include<stdio.h> #include<conio.h> void main() { int a; printf("Enter a Number: "); scanf("%d",&a); if(a > 0) { printf("Given Number is Positive"); } else if(a == 0) { printf("Given Number is Zero"); } else if(a < 0) { printf("Given Number is Negative"); } getch(); }
For Loop Statement in C
The for loop is used in the case where we need to execute some part of the code until the given condition is satisfied. The for loop is also called as a per-tested loop. It is better to use for loop if the number of iteration is known in advance. The for-loop statement is a very specialized while loop, which increases the readability of a program. It is frequently used to traverse the data structures like the array and linked list.
Syntax of For Loop Statement in C
for (initialization; condition test; increment or decrement) { //Statements to be executed repeatedly }
Step 1
First initialization happens and the counter variable gets initialized.
Step 2
In the second step the condition is checked, where the counter variable is tested for the given condition, if the condition returns true then the C statements inside the body of for loop gets executed, if the condition returns false then the for loop gets terminated and the control comes out of the loop.
Step 3
After successful execution of statements inside the body of loop, the counter variable is incremented or decremented, depending on the operation (++ or --).
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/* for loop statement in C language */ // Program to calculate the sum of first n natural numbers // Positive integers 1,2,3...n are known as natural numbers #include <stdio.h> int main() { int num, count, sum = 0; printf("Enter a positive integer: "); scanf("%d", &num); // for loop terminates when num is less than count for(count = 1; count <= num; ++count) { sum += count; } printf("Sum = %d", sum); return 0; }
sizeof() Operator in C
The sizeof() operator is commonly used in C. It determines the size of the expression or the data type specified in the number of char-sized storage units. The sizeof() operator contains a single operand which can be either an expression or a data typecast where the cast is data type enclosed within parenthesis. The data type cannot only be primitive data types such as integer or floating data types, but it can also be pointer data types and compound data types such as unions and structs.
Syntax for sizeof() Operator in C
#include <stdio.h> sizeof (data type)
data type
Where data type is the desired data type including classes, structures, unions and any other user defined data type. Mainly, programs know the storage size of the primitive data types. Though the storage size of the data type is constant, it varies when implemented in different platforms. For example, we dynamically allocate the array space by using sizeof() operator:
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/* return the size of a variable by sizeof() operator example */ int main( int argc, char* argv[] ) { printf("sizeof(char) = %d\n", sizeof(char) ); printf("sizeof(short) = %d\n", sizeof(short) ); printf("sizeof(int) = %d\n", sizeof(int) ); printf("sizeof(long) = %d\n", sizeof(long) ); printf("sizeof(long long) = %d\n", sizeof(long long) ); printf("\n"); printf("sizeof(unsigned char) = %d\n", sizeof(unsigned char) ); printf("sizeof(unsigned short) = %d\n", sizeof(unsigned short) ); printf("sizeof(unsigned int) = %d\n", sizeof(unsigned int) ); printf("sizeof(unsigned long) = %d\n", sizeof(unsigned long) ); printf("\n"); printf("sizeof(float) = %d\n", sizeof(float) ); printf("sizeof(double) = %d\n", sizeof(double) ); printf("sizeof(long double) = %d\n", sizeof(long double) ); printf("\n"); int x; printf("sizeof(x) = %d\n", sizeof(x) ); }
If Else Statement in C
The if-else statement is used to perform two operations for a single condition. The if-else statement is an extension to the if statement using which, we can perform two different operations, i.e., one is for the correctness of that condition, and the other is for the incorrectness of the condition. Here, we must notice that if and else block cannot be executed simiulteneously. Using if-else statement is always preferable since it always invokes an otherwise case with every if condition.
Syntax for if-else Statement in C
if (test expression) { // run code if test expression is true } else { // run code if test expression is false }
If the test expression is evaluated to true, • statements inside the body of if are executed. • statements inside the body of else are skipped from execution. If the test expression is evaluated to false, • statements inside the body of else are executed • statements inside the body of if are skipped from execution.
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/* if else statement in C language */ // Check whether an integer is odd or even #include <stdio.h> int main() { int number; printf("Enter an integer: "); scanf("%d", &number); // True if the remainder is 0 if (number%2 == 0) { printf("%d is an even integer.",number); } else { printf("%d is an odd integer.",number); } return 0; }
scanf() Function in C
Read formatted data from stdin. Reads data from stdin and stores them according to the parameter format into the locations pointed by the additional arguments. The additional arguments should point to already allocated objects of the type specified by their corresponding format specifier within the format string. In C programming, scanf() is one of the commonly used function to take input from the user. The scanf() function reads formatted input from the standard input such as keyboards. The scanf() function enables the programmer to accept formatted inputs to the application or production code. Moreover, by using this function, the users can provide dynamic input values to the application.
Syntax for scanf() Function in C
#include <stdio.h> int scanf ( const char * format, ... );
format
C string that contains a sequence of characters that control how characters extracted from the stream are treated: • Whitespace character: the function will read and ignore any whitespace characters encountered before the next non-whitespace character (whitespace characters include spaces, newline and tab characters -- see isspace). A single whitespace in the format string validates any quantity of whitespace characters extracted from the stream (including none). • Non-whitespace character, except format specifier (%): Any character that is not either a whitespace character (blank, newline or tab) or part of a format specifier (which begin with a % character) causes the function to read the next character from the stream, compare it to this non-whitespace character and if it matches, it is discarded and the function continues with the next character of format. If the character does not match, the function fails, returning and leaving subsequent characters of the stream unread. • Format specifiers: A sequence formed by an initial percentage sign (%) indicates a format specifier, which is used to specify the type and format of the data to be retrieved from the stream and stored into the locations pointed by the additional arguments. A format specifier for scanf follows this prototype: %[*][width][length]specifier
specifier
Where the specifier character at the end is the most significant component, since it defines which characters are extracted, their interpretation and the type of its corresponding argument:
i – integer
Any number of digits, optionally preceded by a sign (+ or -). Decimal digits assumed by default (0-9), but a 0 prefix introduces octal digits (0-7), and 0x hexadecimal digits (0-f). Signed argument.
d or u – decimal integer
Any number of decimal digits (0-9), optionally preceded by a sign (+ or -). d is for a signed argument, and u for an unsigned.
o – octal integer
Any number of octal digits (0-7), optionally preceded by a sign (+ or -). Unsigned argument.
x – hexadecimal integer
Any number of hexadecimal digits (0-9, a-f, A-F), optionally preceded by 0x or 0X, and all optionally preceded by a sign (+ or -). Unsigned argument.
f, e, g – floating point number
A series of decimal digits, optionally containing a decimal point, optionally preceeded by a sign (+ or -) and optionally followed by the e or E character and a decimal integer (or some of the other sequences supported by strtod). Implementations complying with C99 also support hexadecimal floating-point format when preceded by 0x or 0X.
c – character
The next character. If a width other than 1 is specified, the function reads exactly width characters and stores them in the successive locations of the array passed as argument. No null character is appended at the end.
s – string of characters
Any number of non-whitespace characters, stopping at the first whitespace character found. A terminating null character is automatically added at the end of the stored sequence.
p – pointer address
A sequence of characters representing a pointer. The particular format used depends on the system and library implementation, but it is the same as the one used to format %p in fprintf.
[characters] – scanset
Any number of the characters specified between the brackets. A dash (-) that is not the first character may produce non-portable behavior in some library implementations.
[^characters] – negated scanset
Any number of characters none of them specified as characters between the brackets.
n – count
No input is consumed. The number of characters read so far from stdin is stored in the pointed location.
%
A % followed by another % matches a single %. Except for n, at least one character shall be consumed by any specifier. Otherwise the match fails, and the scan ends there.
sub-specifier
The format specifier can also contain sub-specifiers: asterisk (*), width and length (in that order), which are optional and follow these specifications:
*
An optional starting asterisk indicates that the data is to be read from the stream but ignored (i.e. it is not stored in the location pointed by an argument).
width
Specifies the maximum number of characters to be read in the current reading operation (optional).
length
One of hh, h, l, ll, j, z, t, L (optional). This alters the expected type of the storage pointed by the corresponding argument (see below).
... (additional arguments)
Depending on the format string, the function may expect a sequence of additional arguments, each containing a pointer to allocated storage where the interpretation of the extracted characters is stored with the appropriate type. There should be at least as many of these arguments as the number of values stored by the format specifiers. Additional arguments are ignored by the function. These arguments are expected to be pointers: to store the result of a scanf operation on a regular variable, its name should be preceded by the reference operator (&) (see example). On success, the function returns the number of items of the argument list successfully filled. This count can match the expected number of items or be less (even zero) due to a matching failure, a reading error, or the reach of the end-of-file. If a reading error happens or the end-of-file is reached while reading, the proper indicator is set (feof or ferror). And, if either happens before any data could be successfully read, EOF is returned. If an encoding error happens interpreting wide characters, the function sets errno to EILSEQ.
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/* read formatted data from stdin by scanf() function example */ #include <stdio.h> #include <stdlib.h> #include <string.h> int main(int argc, const char * argv[]) { /* Define temporary variables */ char name[10]; int age; int result; /* Ask the user to enter their first name and age */ printf("Please enter your first name and your age.\n"); /* Read a name and age from the user */ result = scanf("%s %d",name, &age); /* We were not able to parse the two required values */ if (result < 2) { /* Display an error and exit */ printf("Either name or age was not entered\n\n"); exit(0); } /* Display the values the user entered */ printf("Name: %s\n", name); printf("Age: %d\n", age); return 0; }
Assignment Operators in C
Assignment operators are used to assign the value, variable and function to another variable. Assignment operators in C are some of the C Programming Operator, which are useful to assign the values to the declared variables. Let's discuss the various types of the assignment operators such as =, +=, -=, /=, *= and %=. The following table lists the assignment operators supported by the C language:
=
Simple assignment operator. Assigns values from right side operands to left side operand
+=
Add AND assignment operator. It adds the right operand to the left operand and assign the result to the left operand.
-=
Subtract AND assignment operator. It subtracts the right operand from the left operand and assigns the result to the left operand.
*=
Multiply AND assignment operator. It multiplies the right operand with the left operand and assigns the result to the left operand.
/=
Divide AND assignment operator. It divides the left operand with the right operand and assigns the result to the left operand.
%=
Modulus AND assignment operator. It takes modulus using two operands and assigns the result to the left operand.
<<=
Left shift AND assignment operator.
>>=
Right shift AND assignment operator.
&=
Bitwise AND assignment operator.
^=
Bitwise exclusive OR and assignment operator.
|=
Bitwise inclusive OR and assignment operator.
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/* assignment operators in C language */ #include <stdio.h> main() { int a = 23; int c ; c = a; printf("Line 1 - = Operator Example, Value of c = %d\n", c ); c += a; printf("Line 2 - += Operator Example, Value of c = %d\n", c ); c -= a; printf("Line 3 - -= Operator Example, Value of c = %d\n", c ); c *= a; printf("Line 4 - *= Operator Example, Value of c = %d\n", c ); c /= a; printf("Line 5 - /= Operator Example, Value of c = %d\n", c ); c = 120; c %= a; printf("Line 6 - %= Operator Example, Value of c = %d\n", c ); c <<= 2; printf("Line 7 - <<= Operator Example, Value of c = %d\n", c ); c >>= 2; printf("Line 8 - >>= Operator Example, Value of c = %d\n", c ); c &= 2; printf("Line 9 - &= Operator Example, Value of c = %d\n", c ); c ^= 2; printf("Line 10 - ^= Operator Example, Value of c = %d\n", c ); c |= 2; printf("Line 11 - |= Operator Example, Value of c = %d\n", c ); }
Logical Operators in C
An expression containing logical operator returns either 0 or 1 depending upon whether expression results true or false. Logical operators are commonly used in decision making in C programming. These operators are used to perform logical operations and used with conditional statements like C if-else statements.
&&
Called Logical AND operator. If both the operands are non-zero, then the condition becomes true.
||
Called Logical OR Operator. If any of the two operands is non-zero, then the condition becomes true.
!
Called Logical NOT Operator. It is used to reverse the logical state of its operand. If a condition is true, then Logical NOT operator will make it false.
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/* logical operators in C language */ #include <stdio.h> main() { int a = 4; int b = 23; int c ; if ( a && b ) { printf("Line 1 - Condition is true\n" ); } if ( a || b ) { printf("Line 2 - Condition is true\n" ); } /* lets change the value of a and b */ a = 2; b = 8; if ( a && b ) { printf("Line 3 - Condition is true\n" ); } else { printf("Line 3 - Condition is not true\n" ); } if ( !(a && b) ) { printf("Line 4 - Condition is true\n" ); } }
Pointers in C Language
Pointers in C are easy and fun to learn. Some C programming tasks are performed more easily with pointers, and other tasks, such as dynamic memory allocation, cannot be performed without using pointers. So it becomes necessary to learn pointers to become a perfect C programmer. Let's start learning them in simple and easy steps. As you know, every variable is a memory location and every memory location has its address defined which can be accessed using ampersand (&) operator, which denotes an address in memory. Consider the following example, which prints the address of the variables defined:
#include <stdio.h> int main () { int var1; char var2[10]; printf("Address of var1 variable: %x\n", &var1 ); printf("Address of var2 variable: %x\n", &var2 ); return 0; }
A pointer is a variable whose value is the address of another variable, i.e., direct address of the memory location. Like any variable or constant, you must declare a pointer before using it to store any variable address. The general form of a pointer variable declaration is:
Syntax for Pointer variable declaration in C
type *var-name;
Here, type is the pointer's base type; it must be a valid C data type and var-name is the name of the pointer variable. The asterisk * used to declare a pointer is the same asterisk used for multiplication. However, in this statement the asterisk is being used to designate a variable as a pointer. Take a look at some of the valid pointer declaration:
int *ip; /* pointer to an integer */ double *dp; /* pointer to a double */ float *fp; /* pointer to a float */ char *ch /* pointer to a character */
The actual data type of the value of all pointers, whether integer, float, character, or otherwise, is the same, a long hexadecimal number that represents a memory address. The only difference between pointers of different data types is the data type of the variable or constant that the pointer points to. There are a few important operations, which we will do with the help of pointers very frequently. (a) We define a pointer variable, (b) assign the address of a variable to a pointer and (c) finally access the value at the address available in the pointer variable. This is done by using unary operator * that returns the value of the variable located at the address specified by its operand. NULL Pointers: It is always a good practice to assign a NULL value to a pointer variable in case you do not have an exact address to be assigned. This is done at the time of variable declaration. A pointer that is assigned NULL is called a null pointer. The NULL pointer is a constant with a value of zero defined in several standard libraries. In most of the operating systems, programs are not permitted to access memory at address 0 because that memory is reserved by the operating system. However, the memory address 0 has special significance; it signals that the pointer is not intended to point to an accessible memory location. But by convention, if a pointer contains the null (zero) value, it is assumed to point to nothing. To check for a null pointer, you can use an 'if' statement as follows:
if(ptr) /* succeeds if p is not null */ if(!ptr) /* succeeds if p is null */
Pointer arithmetic: There are four arithmetic operators that can be used in pointers: ++, --, +, - Array of pointers: You can define arrays to hold a number of pointers. Pointer to pointer: C allows you to have pointer on a pointer and so on. Passing pointers to functions in C: Passing an argument by reference or by address enable the passed argument to be changed in the calling function by the called function. Return pointer from functions in C: C allows a function to return a pointer to the local variable, static variable, and dynamically allocated memory as well.
Advantage of Pointer
1) Pointer reduces the code and improves the performance, it is used to retrieving strings, trees, etc. and used with arrays, structures, and functions. 2) We can return multiple values from a function using the pointer. 3) It makes you able to access any memory location in the computer's memory.
Usage of Pointer
There are many applications of pointers in c language. 1) Dynamic memory allocation: In c language, we can dynamically allocate memory using malloc() and calloc() functions where the pointer is used. 2) Arrays, Functions, and Structures: Pointers in c language are widely used in arrays, functions, and structures. It reduces the code and improves the performance.
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/* working of pointers in C Language */ #include <stdio.h> int main() { int* pc, c; c = 22; printf("Address of c: %p\n", &c); printf("Value of c: %d\n\n", c); // 22 pc = &c; printf("Address of pointer pc: %p\n", pc); printf("Content of pointer pc: %d\n\n", *pc); // 22 c = 11; printf("Address of pointer pc: %p\n", pc); printf("Content of pointer pc: %d\n\n", *pc); // 11 *pc = 2; printf("Address of c: %p\n", &c); printf("Value of c: %d\n\n", c); // 2 return 0; }
#include Directive in C
#include is a way of including a standard or user-defined file in the program and is mostly written at the beginning of any C/C++ program. This directive is read by the preprocessor and orders it to insert the content of a user-defined or system header file into the following program. These files are mainly imported from an outside source into the current program. The process of importing such files that might be system-defined or user-defined is known as File Inclusion. This type of preprocessor directive tells the compiler to include a file in the source code program. Here are the two types of file that can be included using #include: • Header File or Standard files: This is a file which contains C/C++ function declarations and macro definitions to be shared between several source files. Functions like the printf(), scanf(), cout, cin and various other input-output or other standard functions are contained within different header files. So to utilise those functions, the users need to import a few header files which define the required functions. • User-defined files: These files resembles the header files, except for the fact that they are written and defined by the user itself. This saves the user from writing a particular function multiple times. Once a user-defined file is written, it can be imported anywhere in the program using the #include preprocessor.
Syntax for #include Directive in C
#include "user-defined_file"
Including using " ": When using the double quotes(" "), the preprocessor access the current directory in which the source "header_file" is located. This type is mainly used to access any header files of the user's program or user-defined files.
#include <header_file>
Including using <>: While importing file using angular brackets(<>), the the preprocessor uses a predetermined directory path to access the file. It is mainly used to access system header files located in the standard system directories.
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/* #include directive tells the preprocessor to insert the contents of another file into the source code at the point where the #include directive is found. */ // C program to illustrate file inclusion // <> used to import system header file #include <stdio.h> // " " used to import user-defined file #include "process.h" // main function int main() { // add function defined in process.h add(10, 20); // mult function defined in process.h multiply(10, 20); // printf defined in stdio.h printf("Process completed"); return 0; }
While Loop Statement in C
While loop is also known as a pre-tested loop. In general, a while loop allows a part of the code to be executed multiple times depending upon a given boolean condition. It can be viewed as a repeating if statement. The while loop is mostly used in the case where the number of iterations is not known in advance. The while loop evaluates the test expression inside the parentheses (). If test expression is true, statements inside the body of while loop are executed. Then, test expression is evaluated again. The process goes on until test expression is evaluated to false. If test expression is false, the loop terminates.
Syntax of While Loop Statement in C
while (testExpression) { // the body of the loop }
• The while loop evaluates the testExpression inside the parentheses (). • If testExpression is true, statements inside the body of while loop are executed. Then, testExpression is evaluated again. • The process goes on until testExpression is evaluated to false. • If testExpression is false, the loop terminates (ends).
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/* while loop statement in C language */ #include<stdio.h> int main() { int n, num, sum = 0, remainder; printf("Enter a number: "); scanf("%d", &n); num = n; // keep looping while n > 0 while( n > 0 ) { remainder = n % 10; // get the last digit of n sum += remainder; // add the remainder to the sum n /= 10; // remove the last digit from n } printf("Sum of digits of %d is %d", num, sum); // signal to operating system everything works fine return 0; }
main() Function in C
In C, the "main" function is treated the same as every function, it has a return type (and in some cases accepts inputs via parameters). The only difference is that the main function is "called" by the operating system when the user runs the program. Thus the main function is always the first code executed when a program starts. main() function is a user defined, body of the function is defined by the programmer or we can say main() is programmer/user implemented function, whose prototype is predefined in the compiler. Hence we can say that main() in c programming is user defined as well as predefined because it's prototype is predefined. main() is a system (compiler) declared function whose defined by the user, which is invoked automatically by the operating system when program is being executed. Its first function or entry point of the program from where program start executed, program's execution starts from the main. So main is an important function in c , c++ programming language.
Syntax for main() Function in C
void main() { ......... // codes start from here ......... }
void
is a keyword in C language, void means nothing, whenever we use void as a function return type then that function nothing return. here main() function no return any value. In place of void we can also use int return type of main() function, at that time main() return integer type value.
main
is a name of function which is predefined function in C library. • An operating system always calls the main() function when a programmers or users execute their programming code. • It is responsible for starting and ends of the program. • It is a universally accepted keyword in programming language and cannot change its meaning and name. • A main() function is a user-defined function in C that means we can pass parameters to the main() function according to the requirement of a program. • A main() function is used to invoke the programming code at the run time, not at the compile time of a program. • A main() function is followed by opening and closing parenthesis brackets.
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/* basic c program by main() function example */ #include <stdio.h> #include <conio.h> main() { printf (" It is a main() function "); int fun2(); // jump to void fun1() function printf ("\n Finally exit from the main() function. "); } void fun1() { printf (" It is a second function. "); printf (" Exit from the void fun1() function. "); } int fun2() { void fun1(); // jump to the int fun1() function printf (" It is a third function. "); printf (" Exit from the int fun2() function. "); return 0; }
printf() Function in C
Writes the C string pointed by format to the standard output (stdout). If format includes format specifiers (subsequences beginning with %), the additional arguments following format are formatted and inserted in the resulting string replacing their respective specifiers. printf format string refers to a control parameter used by a class of functions in the input/output libraries of C programming language. The string is written in a simple template language: characters are usually copied literally into the function's output, but format specifiers, which start with a % character, indicate the location and method to translate a piece of data (such as a number) to characters. "printf" is the name of one of the main C output functions, and stands for "print formatted". printf format strings are complementary to scanf format strings, which provide formatted input (parsing). In both cases these provide simple functionality and fixed format compared to more sophisticated and flexible template engines or parsers, but are sufficient for many purposes.
Syntax for printf() function in C
#include <stdio.h> int printf ( const char * format, ... );
format
C string that contains the text to be written to stdout. It can optionally contain embedded format specifiers that are replaced by the values specified in subsequent additional arguments and formatted as requested. A format specifier follows this prototype: [see compatibility note below] %[flags][width][.precision][length]specifier Where the specifier character at the end is the most significant component, since it defines the type and the interpretation of its corresponding argument:
specifier
a conversion format specifier.
d or i
Signed decimal integer
u
Unsigned decimal integer
o
Unsigned octal
x
Unsigned hexadecimal integer
X
Unsigned hexadecimal integer (uppercase)
f
Decimal floating point, lowercase
F
Decimal floating point, uppercase
e
Scientific notation (mantissa/exponent), lowercase
E
Scientific notation (mantissa/exponent), uppercase
g
Use the shortest representation: %e or %f
G
Use the shortest representation: %E or %F
a
Hexadecimal floating point, lowercase
A
Hexadecimal floating point, uppercase
c
Character
s
String of characters
p
Pointer address
n
Nothing printed. The corresponding argument must be a pointer to a signed int. The number of characters written so far is stored in the pointed location.
%
A % followed by another % character will write a single % to the stream. The format specifier can also contain sub-specifiers: flags, width, .precision and modifiers (in that order), which are optional and follow these specifications:
flags
one or more flags that modifies the conversion behavior (optional)
-
Left-justify within the given field width; Right justification is the default (see width sub-specifier).
+
Forces to preceed the result with a plus or minus sign (+ or -) even for positive numbers. By default, only negative numbers are preceded with a - sign.
(space)
If no sign is going to be written, a blank space is inserted before the value.
#
Used with o, x or X specifiers the value is preceeded with 0, 0x or 0X respectively for values different than zero. Used with a, A, e, E, f, F, g or G it forces the written output to contain a decimal point even if no more digits follow. By default, if no digits follow, no decimal point is written.
0
Left-pads the number with zeroes (0) instead of spaces when padding is specified (see width sub-specifier).
width
an optional * or integer value used to specify minimum width field.
(number)
Minimum number of characters to be printed. If the value to be printed is shorter than this number, the result is padded with blank spaces. The value is not truncated even if the result is larger.
*
The width is not specified in the format string, but as an additional integer value argument preceding the argument that has to be formatted.
.precision
an optional field consisting of a . followed by * or integer or nothing to specify the precision.
.number
For integer specifiers (d, i, o, u, x, X): precision specifies the minimum number of digits to be written. If the value to be written is shorter than this number, the result is padded with leading zeros. The value is not truncated even if the result is longer. A precision of 0 means that no character is written for the value 0. For a, A, e, E, f and F specifiers: this is the number of digits to be printed after the decimal point (by default, this is 6). For g and G specifiers: This is the maximum number of significant digits to be printed. For s: this is the maximum number of characters to be printed. By default all characters are printed until the ending null character is encountered. If the period is specified without an explicit value for precision, 0 is assumed.
.*
The precision is not specified in the format string, but as an additional integer value argument preceding the argument that has to be formatted.
length
an optional length modifier that specifies the size of the argument.
... (additional arguments)
Depending on the format string, the function may expect a sequence of additional arguments, each containing a value to be used to replace a format specifier in the format string (or a pointer to a storage location, for n). There should be at least as many of these arguments as the number of values specified in the format specifiers. Additional arguments are ignored by the function. If a writing error occurs, the error indicator (ferror) is set and a negative number is returned. If a multibyte character encoding error occurs while writing wide characters, errno is set to EILSEQ and a negative number is returned.
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/* print formatted data to stdout by printf() function example */ #include <stdio.h> int main() { char ch; char str[100]; int a; float b; printf("Enter any character \n"); scanf("%c", &ch); printf("Entered character is %c \n", ch); printf("Enter any string ( upto 100 character ) \n"); scanf("%s", &str); printf("Entered string is %s \n", str); printf("Enter integer and then a float: "); // Taking multiple inputs scanf("%d%f", &a, &b); printf("You entered %d and %f", a, b); return 0; }


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