Let's write a function to calculate the power using a loop, and we will also use the `pow` function from the math library for comparison.

#include <stdio.h>
#include <math.h>

double power(double base, int exponent) {
    double result = 1;
    for (int i = 0; i < exponent; i++) {
        result *= base;
    }
    return result;
}

int main() {
    double base;
    int exponent;
    printf("Enter base and exponent: ");
    scanf("%lf %d", &base, &exponent);

    printf("Using custom function: %.2lf\n", power(base, exponent));
    printf("Using pow function: %.2lf\n", pow(base, exponent));

    return 0;
}
            

This program introduces two methods to calculate power, allowing users to understand both the iterative approach and the use of built-in functions.

Compile the code using GCC or your preferred C compiler:

gcc -o powerCalc powerCalc.c -lm

The `-lm` flag is necessary to link the math library, which includes the `pow` function.

Execute your program to compare the results from both methods:

./powerCalc

This will allow you to verify the correctness and efficiency of the custom power function against the standard library function.