Category: 3. Functions

Function overloading in C++ allows you to define multiple functions with the same name but different parameters. Function overloading is used to achieve polymorphism which is an important concept of object-oriented programming systems.

Syntax for Overloaded Functions

Consider the following two function declarations having the same name but different parameters −

return_type function_name(parameter1);
return_type function_name(parameter2);

Example of Function Overloading

In the following example, we are defining three different functions with the same name but different parameters. This example demonstrates the implementation of function overloading −

Open Compiler

#include<iostream>usingnamespace std;// Adding two integers (Function definition 1)intaddition(int a,int b){return a + b;}// Adding three integers (Function definition 2)intaddition(int a,int b,int c){return a + b + c;}// Adding two floating-point numbers (Function definition 3)floataddition(float a,float b){return a + b;}intmain(){
   cout<<addition(10.5f,20.3f)<<endl;
   cout<<addition(10,20,30)<<endl;
   cout<<addition(10,20)<<endl;return0;}

Output

30.8
60
30

How Function Overloading Works?

In the case of different functions with the same name (function overloading), when the compiler reaches a specific function call, it checks with the different function definition based on the parameters type, order, or number of arguments, and executes the matched function definition.

Example

Let suppose, there are 3 different function definitions to add numbers with different parameters −

// Adding two integers (Function definition 1)intaddition(int a,int b){return a + b;}// Adding three integers (Function definition 2)intaddition(int a,int b,int c){return a + b + c;}// Adding two floating-point numbers (Function definition 3)floataddition(float a,float b){return a + b;}

And, you call the function in the following order −

addition(10.5f, 20.3f); // Function call 1
addition(10, 20, 30); // Function call 2
addition(10, 20); // Function call 3

In the above function calls, function definition will be called in the following order −

• Function call 1 will execute Function definition 3, because here we are passing two float values.
• Function call 2 will execute Function definition 2, because here we are passing three integer values.
• Function call 3 will execute Function definition 1, because here we are passing two integer values.

Function Overloading Based on Number of Parameters

This method involves defining multiple functions with the same name but a different number of parameters.

Syntax

voiddisplay(int a);// takes one parametervoiddisplay(int a,double b);// takes two parameters

Example

The following example demonstrates the function overloading based on the number of parameters −

#include <iostream>usingnamespace std;// Function overloads based on the number of parametersvoiddisplay(int a){
   cout <<"Display with one integer: "<< a << endl;}voiddisplay(int a,double b){
   cout <<"Display with an integer and a double: "<< a <<" and "<< b << endl;}intmain(){// Calls the first overloaddisplay(10);// Calls the second overloaddisplay(10,3.14);double:10and3.14return0;}

Output

Display with one integer: 10
Display with an integer and a double: 10 and 3.14

Function Overloading Based on Different Parameter Types

This method involves defining multiple functions with the same name but different types of parameters.

Syntax

voidshow(int a);// parameter with int type voidshow(double a);// parameter with double type

Example

The following example demonstrates the function overloading based on the different parameter types −

Open Compiler

#include <iostream>usingnamespace std;// Function for integer inputvoidshow(int a){
   cout <<"Integer value: "<< a << std::endl;}// Function for double inputvoidshow(double a){
   cout <<"Double value: "<< a << std::endl;}intmain(){show(10);show(3.14);return0;}

Output

Integer value: 10
Double value: 3.14

Function Overloading Based on Different Parameter Order

This method involves defining multiple functions with the same name but different sequences of parameters.

Syntax

// integer followed by a double, // can be any datatype(bool, char etc)voiddisplay(int a,double b){ 
   cout <<"Integer and Double: "<< a <<", "<< b << endl;}// double followed by an integervoiddisplay(double a,int b){  
   cout <<"Double and Integer: "<< a <<", "<< b << endl;}

Example

The following example demonstrates the function overloading based on the different parameter order −

Open Compiler

#include <iostream>usingnamespace std;voiddisplay(int a,double b){
   cout <<"Integer and Double: "<< a <<", "<< b << endl;}voiddisplay(double a,int b){
   cout <<"Double and Integer: "<< a <<", "<< b <<endl;}intmain(){display(10,3.14);display(3.14,10);return0;}

Output

Integer and Double: 10, 3.14
Double and Integer: 3.14, 10

Use Cases for Function Overloading

Function overloading in C++ is a powerful feature that allows you to use the same function name to perform different tasks based on different parameter lists. This can lead to more readable and maintainable code. Here are some common scenarios and examples where function overloading is useful −

• Different Data Types − Function overloading is useful for handling various data types with a common function name.
• Different Number of Parameters − Function overloading provides flexibility with functions which have varying numbers of parameters.
• Parameter Type and Order − Function overloading handles different parameter types or their order.
• Different Operations − Function overloading supports similar operations for different data types or contexts.
• Variant Contexts − Function overloading provides variations of a function to suit different requirements or levels of detail.

The return statement in C++ is used to exit a function and to send a value back to the function’s caller which is optional depending on requirement. It plays a very important role in controlling the flow of a program and making sure that functions will provide results to other parts of the code.

Syntax

Below is the syntax of using return statement in C++ −

return[expression];

Where, “expression” is optional, specifically used for function. If provided, it specifies the value to be returned to the caller.

Example of return Statement

The following is an example of return statement −

Open Compiler

#include <iostream>usingnamespace std;intsum(int a,int b){// Here, returning sum of a and breturn a + b;}intmain(){// Calling the functionint ans =sum(5,2);
   cout <<"The sum of two integers 5 and 2 is:  "<< ans << endl;// Returning from the main (),// 0 represents execution done without any errorreturn0;}

Output

The sum of two integers 5 and 2 is:  7

Key Aspects of return Statement

1. Function Termination

When a return statement is executed, the function exits immediately, and optionally sends value back to the caller.

2. Returning Types

Return by Value

In this the specified value in return statement is sent back to the caller. This is essential for functions which perform calculations or need to provide results.

intAdd(int a,int b){return a + b;// Returns the sum of a and b}

No Return Value (void)

The functions which are declared with void, the return statement can be used without an expression to exit the function early.

voidGetMessage(){
   cout <<"Hello, TutorialsPoint Learner!";return;// Exits the function}

3. Multiple return Statements

A function may consist of multiple return statements, which we generally get to see within conditional statements.

intmax(int a,int b){if(a > b)return a;elsereturn b;}

4. Returning Objects

Functions can return objects, which can be useful for returning multiple values encapsulated in a class or struct.

structpoint{int x, y;};

point getOrigin(){return{0,0};}

5. Early Exit

The return statement can be used to exit a function early, which is useful for error handling or special conditions.

intdivideInteger(int a,int b){if(b ==0){
  cer &lt;&lt;"Error: Division by zero!"&lt;&lt; endl;return-1;// Shows an error}return a / b;}</code></pre>


Return Types and Value Handling in C++



In C++, the return type of a function determines what kind of value (if any) a function will return to the caller. Proper handling of return types and values is important for making sure that functions behave as expected and integrate smoothly with other parts of the program.



1. Primitive Data Types



Primitive data types are the basic built-in types provided by C++. Common examples are like int, float, double, char etc.



Example



Open Compiler



#include <iostream>usingnamespace std;// created a function which returns an integerintgetSquare(int num){return num * num;}intmain(){int value =5;int result =getSquare(value);// Calling the function and storing its result
   cout <<"The square of "<< value <<" is "<< result << endl;return0;}



Output



The square of 5 is 25




2. User-Defined Types



User-defined types include structs and classes. These types allow you to define complex data structures and customize them as per your specific requirements.



Example with Struct



Open Compiler



#include <iostream>usingnamespace std;structPoint{int x;int y;};
Point createPoint(int x,int y){
   Point p;
   p.x = x;
   p.y = y;return p;// will returns a Point object}intmain(){
   Point p =createPoint(10,20);
   cout <<"Point coordinates: ("<< p.x <<", "<< p.y <<")"<< endl;return0;}



Output



Point coordinates: (10, 20)




Example with Classes



Open Compiler



#include <iostream>usingnamespace std;classrectangle{public:rectangle(int w,int h):width(w),height(h){}intgetArea()const{return width * height;}private:int width;int height;};

rectangle createRectangle(int width,int height){returnrectangle(width, height);// Returns a Rectangle object}intmain(){
   rectangle rect =createRectangle(10,5);
   cout <<"Area of given Rectangle is: "<< rect.getArea()<< endl;return0;}



Output



Area of given Rectangle is: 50




3. References and Pointers



References and pointers are used to refer to variables or objects without making any copies. Which can be useful for efficiency and and easy to modify the original data when needed.



Returning by Reference



Open Compiler



#include <iostream>usingnamespace std;int globalValue =100;int&getGlobalValue(){return globalValue;// Returns a reference to the global variable}intmain(){int& ref =getGlobalValue();
   ref =200;// Modifies the global variable
   cout <<"Global Value: "<< globalValue << endl;return0;}



Output



Global Value: 200




Returning by Pointer



Open Compiler



#include <iostream>usingnamespace std;int*createArray(int size){int* array =newint[size];// Allocating memory dynamicallyfor(int i =0; i < size;++i){
  array&#91;i]= i *10;}return array;// Returning a pointer to the allocated array}intmain(){int* myArray =createArray(5);for(int i =0; i &lt;5;++i){
  cout &lt;&lt; myArray&#91;i]&lt;&lt;" ";}delete&#91;] myArray;// Free dynamically allocated memoryreturn0;}</code></pre>


Output



0 10 20 30 40 

A function is a group of statements that together perform a task. Every C++ program has at least one function, which is main(), and all the most trivial programs can define additional functions.

You can divide up your code into separate functions. How you divide up your code among different functions is up to you, but logically the division usually is such that each function performs a specific task.

A function declaration tells the compiler about a function’s name, return type, and parameters. A function definition provides the actual body of the function.

The C++ standard library provides numerous built-in functions that your program can call. For example, function strcat() to concatenate two strings, function memcpy() to copy one memory location to another location and many more functions.

A function is known with various names like a method or a sub-routine or a procedure etc.

Defining a Function

The general form of a C++ function definition is as follows −

return_type function_name( parameter list ) {
   body of the function
}

A C++ function definition consists of a function header and a function body. Here are all the parts of a function −

• Return Type − A function may return a value. The return_type is the data type of the value the function returns. Some functions perform the desired operations without returning a value. In this case, the return_type is the keyword void.
• Function Name − This is the actual name of the function. The function name and the parameter list together constitute the function signature.
• Parameters − A parameter is like a placeholder. When a function is invoked, you pass a value to the parameter. This value is referred to as actual parameter or argument. The parameter list refers to the type, order, and number of the parameters of a function. Parameters are optional; that is, a function may contain no parameters.
• Function Body − The function body contains a collection of statements that define what the function does.

Example

Following is the source code for a function called max(). This function takes two parameters num1 and num2 and return the biggest of both −

// function returning the max between two numbers
 
int max(int num1, int num2) {
   // local variable declaration
   int result;
 
   if (num1 > num2)
  result = num1;
   else
  result = num2;
 
   return result; 
}

Function Declarations

A function declaration tells the compiler about a function name and how to call the function. The actual body of the function can be defined separately.

A function declaration has the following parts −

return_type function_name( parameter list );

For the above defined function max(), following is the function declaration −

int max(int num1, int num2);

Parameter names are not important in function declaration only their type is required, so following is also valid declaration −

int max(int, int);

Function declaration is required when you define a function in one source file and you call that function in another file. In such case, you should declare the function at the top of the file calling the function.

Calling a Function

While creating a C++ function, you give a definition of what the function has to do. To use a function, you will have to call or invoke that function.

When a program calls a function, program control is transferred to the called function. A called function performs defined task and when it’s return statement is executed or when its function-ending closing brace is reached, it returns program control back to the main program.

To call a function, you simply need to pass the required parameters along with function name, and if function returns a value, then you can store returned value. For example −

#include <iostream>
using namespace std;
 
// function declaration
int max(int num1, int num2);
 
int main () {
   // local variable declaration:
   int a = 100;
   int b = 200;
   int ret;
 
   // calling a function to get max value.
   ret = max(a, b);
   cout << "Max value is : " << ret << endl;
 
   return 0;
}
 
// function returning the max between two numbers
int max(int num1, int num2) {
   // local variable declaration
   int result;
 
   if (num1 > num2)
  result = num1;
   else
  result = num2;
 
   return result; 
}

I kept max() function along with main() function and compiled the source code. While running final executable, it would produce the following result −

Max value is : 200

Function Arguments

If a function is to use arguments, it must declare variables that accept the values of the arguments. These variables are called the formal parameters of the function.

The formal parameters behave like other local variables inside the function and are created upon entry into the function and destroyed upon exit.

While calling a function, there are two ways that arguments can be passed to a function −

By default, C++ uses call by value to pass arguments. In general, this means that code within a function cannot alter the arguments used to call the function and above mentioned example while calling max() function used the same method.

Default Values for Parameters

When you define a function, you can specify a default value for each of the last parameters. This value will be used if the corresponding argument is left blank when calling to the function.

This is done by using the assignment operator and assigning values for the arguments in the function definition. If a value for that parameter is not passed when the function is called, the default given value is used, but if a value is specified, this default value is ignored and the passed value is used instead. Consider the following example −

#include <iostream>
using namespace std;
 
int sum(int a, int b = 20) {
   int result;
   result = a + b;
  
   return (result);
}
int main () {
   // local variable declaration:
   int a = 100;
   int b = 200;
   int result;
 
   // calling a function to add the values.
   result = sum(a, b);
   cout << "Total value is :" << result << endl;

   // calling a function again as follows.
   result = sum(a);
   cout << "Total value is :" << result << endl;
 
   return 0;
}

When the above code is compiled and executed, it produces the following result −

Total value is :300
Total value is :120