Question

Possible Duplicate:
How to modify content of the original variable which is passed by value?

I am building a pretty simple program that calculates the area of a rectangle. Simple enough however, as you will notice I cannot seem to get a return value. I keep seeing 0. There is probably an obvious answer or perhaps there is something I just don’t understand. Heres my code:

#include<stdio.h>

//prototypes
int FindArea(int , int , int);

main()
{

//Area of a Rectangle

  int rBase,rHeight,rArea = 0;

  //get base
  printf("\n\n\tThis program will calculate the Area of a rectangle.");
  printf("\n\n\tFirst, enter a value of the base of a rectangle:");
  scanf(" %d" , &rBase);

  //refresh and get height
  system("cls");
  printf("\n\n\tNow please enter the height of the same rectangle:");
  scanf(" %d" , &rHeight);

  //refresh and show output
  system("cls");
  FindArea (rArea , rBase , rHeight);
  printf("\n\n\tThe area of this rectangle is %d" , rArea);
  getch();

}//end main

int FindArea (rArea , rBase , rHeight)
{
 rArea = (rBase * rHeight);

 return (rArea);

}//end FindArea

Answer 1

You intialize rArea to 0. Then, you pass it into FindArea by value. This means none of the changes to rArea in the function are reflected. You don’t make use of the return value, either. Therefore, rArea stays 0.

Option 1 – Use the return value:

int FindArea(int rBase, int rHeight) {
    return rBase * rHeight;
}

rArea = FindArea(rBase, rHeight);

Option 2 – Pass by reference:

void FindArea(int *rArea, int rBase, int rHeight) {
    *rArea = rBase * rHeight;
}

FindArea(&rArea, rBase, rHeight);