Functions are not executed in the order they are arranged in the source file. In a console program, the first function to be executed is usually the function named main. Under Microsoft Windows the first function to be executed is called WinMain. In order to execute a function, a function call must occur.
A function call is merely the function's name, followed by a set of parentheses. The parentheses contain the function parameters (also known as arguments), if there are any. The parentheses are required, even if there are no parameters.
For example, a function named fn1 with no parameters might be called as a statement, like this:
fn1();
If fn1 takes an integer parameter and produces an integer, then it might be called in an expression such as an assignment statement:
a = b-fn1(5)*2;