Function Declare in C++

In C++, a function is declared using the following syntax:

return_type function_name(parameters){
//function body
}

Here, return_type represents the data type of the value returned by the function. If the function doesn't return anything, void is used.

function_name is the name of the function, and parameters is the list of input parameters passed to the function.

For example, let's declare a function that adds two integers and returns their sum:

int add(int a, int b){
    int sum = a + b;
    return sum;
}

In the above function, int is the return type, add is the function name, and a and b are the input parameters.

Another example of declaring a function that doesn't return anything (i.e., void):

void print_string(string s){
    cout << s << endl;
}

Here, void indicates that the function doesn't return any value. print_string is the function name, and s is the input parameter.

In C++, we can also declare a method, which is a function that is part of a class definition. The syntax for declaring a method in a class is:

class Class_name{
    public:
        return_type method_name(parameters){
            //method body
        }
};

Here, Class_name is the name of the class, return_type is the data type of the value returned by the method (or void if the method doesn't return anything), and method_name is the name of the method.

Let's take an example of declaring a method get_area in a class Rectangle that returns the area of a rectangle:

class Rectangle{
    private:
        int length, width;
    public:
        void set_dimensions(int l, int w){
            length = l;
            width = w;
        }
        int get_area(){
            int area = length * width;
            return area;
        }
};

In the above example, set_dimensions and get_area are methods of class Rectangle. set_dimensions assigns values to the private members length and width. get_area calculates the area of the rectangle and returns its value as an integer.