Compute 5 to the power of 3, but it returns 0. Why?

#include <iostream>

double power (double z, int n)
{
    double result(0.0);
    for (int i = 1; i <= n; i++)
        result *= z;
    return result;
}

int main()
{
    int index(3);
    double x(5.0), 开发者_JS百科double y(0.0);
    y = power (x, index);
    std::cout << y << std::endl;
    return 0;
}

Hello, where is the mistake in this code, please?

Thanks!

Because result is initialised to 0. And as we know, 0 * anything == 0. You need to start at 1.

[In future, please learn how to debug! You would easily have spotted this if you had stepped through your code in a debugger, or added some printf statements to your function.]

Mistake is double result(0.0);. 0 multiplied by anything is 0.

Must be double result(1.0);

In your power function, your result is initialized to be 0.0, then when you multiply it by z n times, you just multiply 0 by z.

You should change double result(1.0);.

Your result should be initialized to 1.0 not to 0.0.