Power Building Exercise in C

Question

I’m starting to learn how to program, so forgive me any more silly mistakes. It’s a simple exercise, doing a C power by setting the base and exponential. Here’s my code:

#include <stdio.h>

int main () {

    int n = 0;
    float x = 0;
    int k = 1;
    float s = 0;
    scanf("%d", &n);
    scanf("%f", &x);

    do{
        if(k!=n){
            k = k + 1; 
            s = x*x + s;
        }
        else { s = x;
        }
    } while( k != n); 

    printf("%f", s);

return 0;

}

Question is that for some reason, from the second operation it multiplies the X as an integer, example:

2.1 3: He should give me 2.1*2.1*2.1 = 9.26

Instead he gives me 2.1*2.1*2 = 8.82

Does anyone have any idea why this is and how to fix it?

Answer 1

In the variable s, you should be multiplying x and not x*x. Besides, it shouldn’t be adding up anything (that + s).

Here is your revised program. It also works for negative whole powers:

#include <stdio.h>

int main() {
    int n = 0;
    float x = 0;
    int k = 1;
    float s = 1.0;
    scanf("%d", &n);
    scanf("%f", &x);

    if (n > 0) {
        for (int k = 0; k < n; k++) {
            s *= x;
        }
    } else if (n < 0) {
        for (int k = 0; k < -n; k++) {
            s /= x;
        }
    }

    printf("%f", s);

    return 0;
}

See here working on ideone.

In case you don’t know, s *= x amounts to s = s * x, the s /= x amounts to s = s / x and the k++ amounts to k = k + 1. The use of for is equivalent to that of while in this context, and once it is understood, it is simpler to evaluate mentally as to its correctness.