Passing by Value

Question

So, Sololearn uses this code as an example for passing by value in c++:
void myFunc(int x) {
x = 100;
}
int main() {
int var = 20;
myFunc(var);
cout << var;
}
// Outputs 20
My first question is: For what reason is the 100 there, if we dont use it at all?
And my second question is: Is there anyway of calling the 'x' with cout. Because when I try to output the x and the var at once in the main function, it tells me that x was not declared, even though we declare it at the start.
Because if not, the x at the start kinda feels useless in that case.

Answer 1

1st question: sometimes you want to change var to check something but you don't want to change it in main, just in that function = pass by value
2nd question: x is only visible in myfunc so cout it inside that function, when you return from myfunc to main, program doesn't remember x anymore

Answer 2

Thanks for the quick answer