Question

Why this program only works when I initialize a and b.
I want to pass it without initializing a and b, for example:

numChange(10,15);

Is this possible ?

#include <iostream>
using namespace std;
void numChange(int *x,int *y)
{
     *x = 99;
     *y = 77;
}

int main()
{
    numChange(10,15);
    //int a=10;
    //int b=15;
    //numChange(&a,&b);
    cout<<a<<" , "<<b<<endl;

    return 0;
}

Answer 1

Because you have defined your function to receive pointers, but when you call that function you are trying to pass an int.

The compiler is expecting memory addresses and you are trying to pass constants.

It does not make sense, you are trying to do something like 10 = 99; 15 = 77;?

numChange(10,15);
    //int a=10;
    //int b=15;

It seems that you are hopping that a = 10 = 99 and b = 15 = 77;

If this was possible, it means that I could never (after the call of numChange(10,15);) make a variable to actually have the value 10 because 10 is “pointing” to 99 (is not).