can anyone explain why this program isn't working ? and how to retify this error?

Question

#include<iostream>
using namespace std;

int fun(int &x)
{
return x;
}
int main()
{
cout << fun(10);
return 0;
}

Answer 1

Adding to Sarada Lakshmi suggestion,

int fun( int& x )

Means function `fun` requires <x> to be a readable & writable reference to an `int` variable. And also means function `fun` *may* modify <x> argument somehow.

fun( 10 )

Means to call function `fun` and pass an `int` literal (read-only data) as argument for function fun.

Function `fun` expected a readable & writable `int` reference, but it received instead a literal (read-only data), so it gives a warning.

Answer 2

#include<iostream>
using namespace std;

int fun(int x)
{
return x;
}
int main()
{
cout << fun(10);
return 0;
}

Take by value or by const reference, unless you intend to do something.