This C program reads a sequence of positive integers as input by the user and print their sum. The program keeps on taking the input from user until user enters number ( 0 ) and program calculates the sum of all input numbers. Finally this C program prints the sum of all the numbers on screen and terminates.

This program is an excellent demonstration of using do-while loop of C Programming.

#include <stdio.h>

#define SENTINEL 0

int main(void) {
  int sum = 0; /* The sum of numbers already read */
  int current; /* The number just read */

  do {
    printf("\nEnter an integer > ");
    scanf("%d", &current);
    if (current > SENTINEL)
      sum = sum + current;
  } while (current > SENTINEL);
  printf("\nThe sum is %d\n", sum);
}

Sample output of the C Program is:

Enter an integer > 3
Enter an integer > 4
Enter an integer > 6
Enter an integer > 7
Enter an integer > 8
Enter an integer > 45
Enter an integer > 56
Enter an integer > 0 

The sum is 129