C Program to Calculate the Sum of Natural Numbers

The positive numbers 1, 2, 3... are known as natural numbers. The sum of natural numbers up to 10 is:

sum = 1 + 2 + 3 + ... + 10â€‹

Sum of Natural Numbers Using for Loop :

Program :

#include <stdio.h>
int main() {
    int n, i, sum = 0;

    printf("Enter a positive integer: ");
    scanf("%d", &n);

    for (i = 1; i <= n; ++i) {
        sum += i;
    }

    printf("Sum = %d", sum);
    return 0;
}

Output :

Enter a positive integer: 6
Sum = 21

Sum of Natural Numbers Using while Loop :

Program :

#include <stdio.h>
int main() {
    int n, i, sum = 0;
    printf("Enter a positive integer: ");
    scanf("%d", &n);
    i = 1;

    while (i <= n) {
        sum += i;
        ++i;
    }

    printf("Sum = %d", sum);
    return 0;
}

Output :

Enter a positive integer: 12
Sum = 78

* In both programs, the loop is iterated n number of times. And, in each iteration, the value of i is added to sum and i is incremented by 1.

* Though both programs are technically correct, it is better to use for loop in this case. It's because the number of iterations is known.

Read Input Until a Positive Integer is Entered :

#include <stdio.h>
int main() {
    int n, i, sum = 0;

    do {
        printf("Enter a positive integer: ");
        scanf("%d", &n);
    } while (n <= 0);

    for (i = 1; i <= n; ++i) {
        sum += i;
    }

    printf("Sum = %d", sum);
    return 0;
}â€‹

Output :

Enter a positive integer: 4
Sum = 10â€‹