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 + ... + 10

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Sum of Natural Numbers Using for Loop

#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;
}

The above program takes input from the user and stores it in the variable n. Then, for loop is used to calculate the sum up to n.

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Sum of Natural Numbers Using while Loop

#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: 100
Sum = 5050