- C++ Data Structures
- C++ Basic Input/Output
- C++ Date & Time
- C++ References
- C++ Pointers
- C++ Strings
- C++ Arrays
- C++ Numbers
- C++ Functions
- C++ Decision Making
- C++ Loop Types
- C++ Operators
- C++ Storage Classes
- C++ Modifier Types
- C++ Constants/Literals
- C++ Variable Scope
- C++ Variable Types
- C++ Data Types
- C++ Comments
- C++ Basic Syntax
- C++ Environment Setup
- C++ Overview
- C++ Home
C++ Object Oriented
- C++ Interfaces
- C++ Encapsulation
- C++ Abstraction
- C++ Polymorphism
- C++ Overloading
- C++ Inheritance
- C++ Classes & Objects
C++ Advanced
- C++ Web Programming
- C++ Multithreading
- C++ Signal Handling
- C++ Preprocessor
- C++ Templates
- C++ Namespaces
- C++ Dynamic Memory
- C++ Exception Handling
- C++ Files and Streams
C++ Useful Resources
- C++ Discussion
- C++ Useful Resources
- C++ Standard Library
- C++ STL Tutorial
- C++ Object Oriented
- C++ Quick Guide
- C++ Questions and Answers
Selected Reading
- Who is Who
- Computer Glossary
- HR Interview Questions
- Effective Resume Writing
- Questions and Answers
- UPSC IAS Exams Notes
C++ Functions
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 spanide up your code into separate functions. How you spanide up your code among different functions is up to you, but logically the spanision 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 pbrary 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 pke 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 pst ) { 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 pst together constitute the function signature.
Parameters − A parameter is pke 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 pst 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 pst );
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 vapd 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 calpng the function.
Calpng 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; // calpng 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 pke other local variables inside the function and are created upon entry into the function and destroyed upon exit.
While calpng a function, there are two ways that arguments can be passed to a function −
Sr.No | Call Type & Description |
---|---|
1 | This method copies the actual value of an argument into the formal parameter of the function. In this case, changes made to the parameter inside the function have no effect on the argument. |
2 | This method copies the address of an argument into the formal parameter. Inside the function, the address is used to access the actual argument used in the call. This means that changes made to the parameter affect the argument. |
3 | This method copies the reference of an argument into the formal parameter. Inside the function, the reference is used to access the actual argument used in the call. This means that changes made to the parameter affect the argument. |
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 calpng 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 calpng 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; // calpng a function to add the values. result = sum(a, b); cout << "Total value is :" << result << endl; // calpng 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 :120Advertisements