Code

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

»  if (base==0.0&&exponent<0) {
»    printf("WARNING: mypow called with zero base and negative exponent\n");
»    return 0.0;
  }

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

 int main(){
»  double result;/* The same name as inside mypow() */

»  mypow(7.2, 4);

»  printf("7.2 to the power 4 is %g\n", result);/* Wrong! */

»  return 0;
}
 ...