Tutorial dan Contoh Functions Pemrograman C+

# include <iostream>
#include <cmath>
using namespace std;
int main() {
    double number, squareRoot;
    cout<<"Enter a number: ";
    cin>>number;
/* sqrt() is a library function to calculate square root */
    squareRoot = sqrt(number);
    cout<<"Square root of "<<number<<" = "<<squareRoot;
    return 0;
}

Enter a number: 26
Square root of 26 = 5.09902

Consider the figure above. When a program begins running, the system calls the main() function, that is, the system starts executing codes from main() function. When control of program reaches to function_name() inside main(), the control of program moves to void function_name(), all codes inside void function_name() is executed and control of program moves to code right after function_name() inside main() as shown in figure above.

Example 1: Function

# include <iostream>
using namespace std;
int add(int, int);            //Function prototype(declaration)
int main() {
    int num1, num2, sum;
    cout<<"Enters two numbers to add: ";
    cin>>num1>>num2;
    sum = add(num1,num2);         //Function call
    cout<<"Sum = "<<sum;
    return 0;
}
int add(int a,int b) {            //Function declarator
    int add;
    add = a+b;
    return add;                 //Return statement
}

Enters two integers: 8
-4
Sum = 4

Function prototype(declaration)

If an user-defined function is defined after main() function, compiler will show error. It is because compiler is unaware of user-defined function, types of argument passed to function and return type.
In C++, function prototype is a declaration of function without function body to give compiler information about user-defined function. Function prototype in above example:

int add(int, int);

You can see that, there is no body of function in prototype. Also there are only return type of arguments but no arguments. You can also declare function prototype as below but it's not necessary to write arguments.

int add(int a, int b);

Function Call

To execute the codes of function body, the user-defined function needs to be invoked(called). In the above program, add(num1,num2); inside main() function calls the user-defined function. In the above program, user-defined function returns an integer which is stored in variable add.

Function Definition

The function itself is referred as function definition. Function definition in the above program:

/* Function definition  */

int add(int a,int b) {      // Function declarator
    int add;
    add = a+b;
    return add;             // Return statement
}

When the function is called, control is transferred to first statement of function body. Then, other statements in function body are executed sequentially. When all codes inside function definition is executed, control of program moves to the calling program.

Passing Arguments to Function

In programming, argument(parameter) refers to data this is passed to function(function definition) while calling function.
In above example, two variables, num1 and num2 are passed to function during function call. These arguments are known as actual arguments. The value of num1 and num2 are initialized to variables a and b respectively. These arguments a and b are called formal arguments. This is demonstrated in figure below:

return add;