C++ : Confused on something about functions

#include <iostream>
using namespace std;

int myFunc (unsigned short int x );

int main ()
{
    unsigned short int x, y;
    x=7;
    y = myFunc(x);
    std::cout << "x:" << x << "y: " <开发者_如何学JAVA< y << "\n";
    return 0;
}

int myFunc (unsigned short int x )
{
    return (4 * x );
}

Now this ^ Code works, but when I change

y = myFunc(x);

into

y = myFunc(int);

it will no longer work, why is that?

y =myFunc(int);

This is not a valid expression. int is a type, you cannot pass a type as an argument to a function.

if
x=7;

y = myFunc(x); is equal to y = myFunc(7);

if you use int, what value it has? so the error occurs

Because int is a reserved word. And even if it wasn't - you haven't declared (and defined) identifier called "int".

That's because the compiler expects the value of type unsigned short int, but you've passed a type int. What did you expected to get? The result of 4*int is undefined.

You can pass types when you use templates. Take a look on the following sample:

// Here's a templated version of myFunc function 
template<typename T>
T myFunc ( unsigned short int x )
{
    return (4 * x );
}

...

y = myFunc<int>( x ); // here you can pass a type as an argument of the template,
// but at the same moment you need to pass a value as an argument of the function