1. C++ Tutorials

What is a function declaration in Cpp

A function features a name and a kind , very similar to a variable. The function’s type is defined by its return value, that is, the worth the function passes back to the program. In addition, the type of arguments required by a function is important.

When a function is declared, the compiler must therefore be given information on.

  • the name and type of the function and
  • the type of each argument

This is also referred to as the function prototype.

int toupper(int);
double pow(double, double);

This informs the compiler that the function toupper() is of type int, i.e. its return
value is of type int, and it expects an argument of type int.

The second function pow() is of type double and two arguments of type double must be passed to the function when it is called.

The types of the arguments could also be followed by names, however, the names are viewed as a comment only.

int toupper(int c);
double pow(double base, double exponent);

From the compiler’s point of view, these prototypes are equivalent to the prototypes
in the previous example. Both junctions are standard junctions.

Standard function prototypes don’t got to be declared, nor should they be, as they have already been declared in standard header files.

If the header file is included in the program’s source code by means of the #include directive, the function can be used immediately.


Using Function And Classes Sample program


using namespace std;
int main()
double x = 2.5, y;
// By means of a prototype, the compiler generates
// the correct call or an error message!
// Computes x raised to the power 3:

y = pow("x", 3.0); // Error! String is not a number
y = pow(x + 3.0); // Error! Just one argument
y = pow(x, 3.0); // ok!
y = pow(x, 3); // ok! The compiler converts the

// int value 3 to double.
cout << "2.5 raised to 3 yields:

<< y << endl;
// Calculating with pow() is possible:
cout << "2 + (5 raised to the power 2.5) yields: "
<< 2.0 + pow(5.0, x) << endl;
return 0;

Screen output
2.5 raised to the power 3 yields: 15.625
2 + (5 raised to the power 2.5) yields: 57.9017

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