Function is a small sub program , which is designed to perform a particular task in a complete program and it is designed in this way that it can be coupled with another function.
return type function_name ( argument)
{
statement; function Syntax
}
where
return type : Data type of the value return by the function
function_name : Any Valid identifier
Statement : Any Valid C/C++ statement(s)
Our first Function : To print “hello world” on the screen
| void print_message(void) { cout<<”\n Hello world”; return ; } |
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| NOTE : return is not compulsory, but good programming skill recommends every function should have a return. |
How to implement this function in a C++ program
| Method -1 | Method-2 |
| #include<iostream> #include<conio.h> using namespace std; void print_message(void) { cout<<"\n Hello world"; return; } int main() { print_message(); getch(); return 0; } | #include<iostream> #include<conio.h> using namespace std; void print_message(void); // function prototype int main() { print_message(); // function call getch(); return 0; } void print_message(void) { cout<<"\n Hello world"; return; } |
Function Prototype: A function prototype in C or C++ is a declaration of a function that omits the function
body but does specify the function's name, argument types and return type. While a
function definition specifies what a function does, a function prototype can be
thought of as specifying its interface.
TYPE-I
Solution
| Program | Output |
| #include<iostream> #include<conio.h> using namespace std; void area_triangle(void) { int b,h,ar; system("cls"); // clrscr() cout<<"\n Enter base :"; cin>>b; cout<<"\n Enter height :"; cin>>h; ar =0.5*b*h; cout<<"\n Area of Triangle :"<<ar; return; } int main() { area_triangle(); // function Call getch(); return 0; } |
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NOTE : main( ) is also a function. It has the following feature
without main program can not execute.
A program can have more than one function but can not have more than one main ( )
Program execution begin from main( )
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Type –II Problem : Write a function in C++ to read base and height of a right angle triangle, calculate area of triangle using formula area = ½*b*h and return it to it’s calling function. Also implement this function in a C++ program
Solution
| Program | Output |
| #include<iostream> #include<conio.h> using namespace std; int area_triangle(void) { int b,h,ar; cout<<"\n Enter base :"; cin>>b; cout<<"\n Enter Height :"; cin>>h; ar =int(0.5*b*h); return (ar); } int main() { int res =area_triangle(); cout<<"\n Area of Triangle :"<<res; getch(); return 0; } |
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Type –III Problem : Define a function in C++ Area_triangle( ) which accept two integer type parameter (i) int base (ii) int height. This function calculates area of Triangle using formula area = 1/2*base*height and also display this calculated area on the screen. Also implement this function in C++ program
Solution
| Program | Output |
| #include<iostream> #include<conio.h> using namespace std; void area_triangle(int base, int height) { int ar; ar =int(0.5*base*height); cout<<"\n Area of Triangle :"<<ar; } int main() { area_triangle(10,20); getch(); return 0; } |
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Type –IV
TYPE –IV Problem : Write a user defined function in C++ Area_Triangle( ) which accept two integer type parameter (i) int base (ii) int height. This function calculates area of triangle using formula area = ½*base*height and return it to it’s calling function. Also implement this function in C++ program
Solution
| Problem | Output |
| #include<iostream> #include<conio.h> using namespace std; int area_triangle(int base, int height) { int ar; ar =int(0.5*base*height); return(ar); } int main() { int res =area_triangle(10,20); cout<<"\n Area of Triangle :"<<res; getch(); return 0; } |
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Parameter Types
- Call by Value method
- Call By reference method
Call By Value Method: In this method actual parameter make it’s copy and send to formal parameter. The processing inside function use this copy of actual parameter. So the changes made inside function does not automatically available to it’s calling function.
| Program | Output |
| #include<iostream> #include<conio.h> using namespace std; void add ( int a) // formal Parameter { a = a+10; } int main() { int x=10; cout<<"\nBefore function call x :"<<x; add(x); cout<<"\nafter function call x :"<<x; getch(); return 0; } |
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Call By reference Method : In this method actual parameter pass the address of actual parameter. So the changes made inside function is automatically available to it’s calling function.
| Program | output |
| #include<iostream> #include<conio.h> using namespace std; void add ( int &a) // Call by reference { a = a+10; } int main() { int x=10; cout<<"\nBefore function call x :"<<x; add(x); cout<<"\nafter function call x :"<<x; getch(); return 0; } NOTE : in case of reference type parameter, actual parameter must be of variable type |
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Scope of Variable
- Auto / Local Variable : The variable whose life begins within opening curly braces and it dies at the position of it’s corresponding curly braces, is called local variable
- Global Variable : The variable whose scope is whole program , and is defined outside function ,is called global variable
| Program | Output |
| #include<iostream> #include<conio.h> using namespace std; int a=20; // Global Variable int main() { int a=10; // Local Variable { int a=30; cout<<"\n Value of a :"<<::a; } cout<<"\n Value of a :"<<a; getch(); return 0; } |
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- Static Variable : These are local variable to that function where it is defind , but does not loose their values between the function call.
| Example Program | Output |
| #include<iostream> #include<conio.h> using namespace std; void show(void) { static int a=0; a++; cout<<"\n Value of a :"<<a; } int main() { show(); show(); show(); getch(); return 0; } |
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Parameter with default Values
| Exmaple Program | Output |
| #include<iostream> #include<conio.h> using namespace std; void show(int a=10) { cout<<"\n Value of a :"<<a; } int main() { show(); show(30); getch(); return 0; } |
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Some Additional Definition_______________________________________________________________
Formal Parameter : The parameter which appears with function prototype is called formal parameter.
Actual parameter : The Parameter which is used at the time of call function , is called actual parameter
Example
#include<iostream>
#include<conio.h>
void show ( int a) // here a is formal parameter
{
………….
………….
}
int main( )
{
int x =10;
Show (x) ; // x is here actual parameter.
………….
…………
}
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