Sum of N numbers without mutating any variables.

sumOfN.c

#include<stdio.h>

int sum(int n) {
  if (n == 1) return 1;
  else return n + sum(n - 1);
}

int main() {
    int input;
    scanf("%d", &input);
    const int s = sum(input);
    printf("%d\n", s);
}