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A simple four-function calculator



A simple four-function calculator

#include <stdio.h>
#include <stdlib.h>

#define MAX 100

int *p;   /* will point to a region of free memory */
int *top-of-stack ; 
int *bottom-of-stack; 

void push(int i)
{
  if(p > bottom-of-stack) {
    printf("Stack Full\n");
    return;
  }
  *p = i;
  p++;
}

int pop(void)
{
  p--;
  if(p < top-of-stack ) {
    printf("Stack Underflow\n");
    return 0;
  }
  return *p;
}

int main(void)
{
  int x, y;
  char s[80];

  p = (int *) malloc(MAX*sizeof(int)); /* get stack memory */
  if(!p) {
    printf("Allocation Failure\n");
    exit(1);
  }
  top-of-stack  = p;
  bottom-of-stack = p + MAX-1;

  printf("Four Function Calculator\n");
  printf("Enter 'q' to quit\n");

  do {
    printf(": ");
    gets(s);
    switch(*s) {
      case '+':
        x = pop();
        y = pop();
        printf("%d\n", x+y);
        push(x+y);
        break;
      case '-':
        x = pop();
        y = pop();
        printf("%d\n", y-x);
        push(y-x);
        break;
      case '*':
        x = pop();
        y = pop();
        printf("%d\n", y*x);
        push(y*x);
        break;
      case '/':
        x = pop();
        y = pop();
        if(x==0) {
          printf("Divide by 0.\n");
          break;
        }
        printf("%d\n", y/x);
        push(y/x);
        break;
      case '.': /* show contents of top of stack */
        x = pop();
        push(x);
        printf("Current value on top of stack: %d\n", x);
        break;
      default:
        push(atoi(s));
    }
  } while(*s != 'q');

  return 0;
}