Functions: a complete example using prototypes

Comments and questions to John Rowe.

The following example is intended to show main() calling a function that in turn calls another function:

1. main() calls the function printexp(double x, int j) whose job is to print out x to the power j.
2. printexp() in turn calls mypow() to do the actual calculation.

//
// Demonstrate function prototypes
//
#include <stdio.h>

double mypow(double base, int exponent);
void printexp(double x, int j);

int main() {
  double base = 5.3;
  int n = 2;

  printexp(base, n); 

  return 0; 
}


//
// Print out x to the power j, warning if x and j are invalid
//
void printexp(double base, int j) {
  if ( base == 0.0 && j < 0 ) {
    printf("Invalid values to printexp\n");
    return;
  }
  printf("%f to the power %d is %f\n", base, j, 
         mypow(base, j));
}


//
// Return base to the power of exponent.
// If base == zero and exponent < zero, return zero
//
double mypow(double base, int exponent) {
  double result = 1.0;

  if (base == 0.0 && exponent < 0 ) 
    return 0.0;

  while (exponent > 0) {
    result *= base;
    --exponent;
  }
  
  while (exponent < 0) {
    result /= base;
    ++exponent;
  }
  
  return result;
}

Step through this code