C Programming Code Examples C > For Loops and While Loops Code Examples convert Octal to Decimal number system convert Octal to Decimal number system Write a C program to input Octal number from user and convert to Decimal number system. How to convert from Octal number system to Decimal number system in C program. Octal number system Octal number system is a base 8 number system. Octal number system uses 8 symbols to represent all its numbers i.e. 01234567 Decimal number system Decimal number system is a base 10 number system. Decimal number system uses 10 symbols to represent all its numbers i.e. 0123456789 Algorithm Conversion Octal to Binary begin: read(octal); decimal = 0; rem = 0; place = 0; While(octal !=0) begin: rem = octal % 10; decimal = decimal + (8place * rem); octal = octal / 10; place = place + 1; end; write('Decimal =' decimal); end; #include <stdio.h> #include <math.h> int main() { long long octal, tempOctal, decimal; int rem, place; /* Input octal number from user */ printf("Enter any octal number: "); scanf("%lld", &octal); tempOctal = octal; decimal = 0; place = 0; /* Convert octal to decimal */ while(tempOctal > 0) { /* Extract the last digit of octal */ rem = tempOctal % 10; /* Convert last octal digit to decimal */ decimal += pow(8, place) * rem; /* Remove the last octal digit */ tempOctal /= 10; place++; } printf("Octal number = %lld\n", octal); printf("Decimal number = %lld", decimal); return 0; }