Why Isn't My C++ Function Passing By Reference Correctly?

[Colton0117]

Define a function CoordTransform() that transforms its first two input parameters xVal and yVal into two output parameters xValNew and yValNew. The function returns void. The transformation is new = (old + 1) * 2. Ex: If xVal = 3 and yVal = 4, then xValNew is 8 and yValNew is 10.

My code:

#include <iostream>
using namespace std;

void CoordTransform(int xVal , int yVal , int xValNew, int yValNew){ 
    
   xValNew = (xVal +1) *2;
   yValNew = (yVal +1) *2;  
   return;
}

int main() {
   int xValNew = 0;
   int yValNew = 0;

   CoordTransform(3, 4, xValNew, yValNew);
   cout << "(3, 4) becomes " << "(" << xValNew << ", " << yValNew << ")" << endl;

   return 0;
}

My output is (3, 4) becomes (0, 0) when it should be (8, 10), what am I missing or overlooking to operate the void and have x or y ValNew hold its value?

 

[MarkFL]

It looks like an issue of variable scope. The values you are passing to your function are then local to the function. You may need to either make the variables containing the new values global, or return them explicitly. :)

 

[Colton0117]

Thanks, the issue was the void it should be:

void CoordTransform(int x ,int y ,int& xValNew,int& yValNew)

needed the & after the int

 

[MarkFL]

Thanks, the issue was the void it should be:

void CoordTransform(int x ,int y ,int& xValNew,int& yValNew)

needed the & after the int

Yes, basically the "&" says "don't make a copy of this variable, use the same variable." :)