In C++, there are broadly two types of functions :
These functions are part of the compiler package. These are part of standard library made available by the compiler. For example, exit(), sqrt(), pow(), strlen() etc. are library functions (built-in functions). Built-in functions are already discussed in C++ Standard Library Functions Tutorial.
Built-in functions helps you, to use function without declaring and defining it. To use built-in functions in a program, you have to only include that header file where the required function is defined. Here is an example. This program uses built-in function named strlen() of string.h header file to find the length of the string.
/* C++ Function Types - C++ Built-in Function */
#include<iostream.h>
#include<string.h>
#include<conio.h>
void main()
{
clrscr();
char str[80];
cout<<"Enter any string (line):\n";
cin.getline(str, 80);
int len = strlen(str);
cout<<"\nLength of the string is: "<<len;
getch();
}
Here is the sample run of the above C++ program, finds the length of the string entered by the user
The user-defined functions are created by you i.e., the programmer. These functions are created as per requirements of your program. Here is an example, demonstrating user-defined functions in C++
/* C++ Function Types - C++ User-defined Function */
#include<iostream.h>
#include<conio.h>
void start_msg(void); // function declaration
void main()
{
clrscr();
start_msg(); // function calling
int num;
cout<<"Enter a number: ";
cin>>num;
cout<<"You entered: "<<num;
getch();
}
void start_msg(void) // function definition
{
cout<<"Welcome to codescracker.com\n";
cout<<"This is C++ Function Types Tutorial\n\n";
}
Here is the sample output of the above C++ program:
Here is another program in C++, also demonstrating user-defined function
/* C++ Function Types - C++ User-defined Function */
#include<iostream.h>
#include<conio.h>
void greeting(void);
void main()
{
clrscr();
char ch;
cout<<"Press y for greeting: \n";
cin>>ch;
if(ch=='y' || ch=='Y')
{
greeting();
}
cout<<"Want to learn more ? (y/n).. ";
cin>>ch;
if(ch=='y' || ch=='Y')
{
cout<<"Yep..!!..You can proceed..!!\n";
}
else
{
cout<<"Sure..!!..You can take rest..!!\n";
}
getch();
}
void greeting(void)
{
cout<<"Welcome to codescracker.com";
cout<<"\nYou are at good position now\n\n";
}
Here are some sample runs of the above C++ program:
Let's take another program, for complete understanding of user-defined functions in C++
/* C++ Function Types - C++ User-defined Function */
#include<iostream.h>
#include<conio.h>
void msg(void);
int add(int, int);
void main()
{
clrscr();
msg();
int a, b;
cout<<"Enter any two number: ";
cin>>a>>b;
cout<<"The sum of the two numbers is: "<<add(a, b);
getch();
}
void msg(void)
{
cout<<"Welcome to codescracker.com";
cout<<"\nThis is addition program\n\n";
}
int add(int x, int y)
{
return x+y;
}
Below is the sample output of this C++ program:
