Function
1.It is a collection of statements that performs an specific task.
2.It executes when it is called by its name.
3.A large program is divided into a number of small building block
for simplicity and this building block is called function.
4.We can call a function again and again.
5.The most important features of function is code reusability.
6.The C library provides many pre-defined functions.
Syntax of Function
Description
| return type |
1.It is a keyword which indicates that which type of value is being returning by the function. 2.If we do not to return any value then we use void keyword in place of return_type. |
| function name |
1.It is the actual name of the function. 2.It is also used at the time of calling the function. |
| parameter list |
1.It is the place where we can pass a number of parameter/variable. 2.These variables may be used in the program. 3.The value of parameter can be initialized or we can pass it from the calling of function. 4.It is optional part. |
| body | It is the place where the actual code is written to perform the specific task. |
Key point about the function.
Function Declaration:
At this stage the function is declared .For example :
void add();
This is a function declaration in which void(no return type) indicates there is no value returning by this function and add is the name of function.
Note-It is optional.
Function Definition:
This is the place where actual code is written to perform the task. For example :
void add() { int x,y=20,z=30; x=y+z; printf("Add=%d",x); }
This is a function definition and here we can see that code is written to perform the addition task.
Function Calling:
At this stage the function is called .For example :
add();
To call a function just write function name and put semi-colon(;) after it.
Complete Example
#include<stdio.h> void add();//function declaration void add()//function definition { int x,y=20,z=30; x=y+z; printf("Add=%d",x); } int main() { add();//function calling } /* ###Output### Add=50 */
Types of Function
printf(),scanf(),clrscr(),getch() etc.
User-defined Function
The function which is made by the user is called user-defined function. for example:-add(),sub(),multi(),div()[Note: These are user-defined name.it may different.] etc.
Category of User-defined Function
There are four category of user-defined function1. Function with no return type and no parameter.
2. Function with no return type and with parameter.
3. Function with return type and no parameter.
4. Function with return type and with parameter.
Function with no return type and no parameter
The function in which there is no parameter and there is no value returning by that function is called Function with no return type and no parameter.
#include<stdio.h> void add();//function declaration void add()//function definition { int x,y=20,z=30; x=y+z; printf("Add=%d",x); } int main() { add();//function calling } /* ###Output### Add=50 */
Function with no return type and with parameter
The function in which there is some parameter and there is no value returning by that function is called Function with no return type and with parameter.
#include<stdio.h> void add(int y,int z);//function declaration void add(int y,int z)//function definition { int x; x=y+z; printf("Add=%d",x); } int main() { //here 20 will assign to y and 30 to z add(20,30);//function calling } /* ###Output### Add=50 */
In the above example there are two parameter of integer type namely y and z there at the time of calling two integer value will be passed in which first will assign to y and second will assign to z.
Function with return type and no parameter
The function in which there is no parameter and there is some value returning by that function is called Function with return type and no parameter.
#include<stdio.h> int add();//function declaration int add()//function definition { int x,y=20,z=30; x=y+z; //return value of x return x; } int main() { //assigning return value to variable rs int rs=add();//function calling printf("Add=%d",rs); } /* ###Output### Add=50 */
In the above example there is no parameter but the function will return integer value because there is int keyword in the place of return type and returned value will assign to variable rs.
Function with return type and with parameter
The function in which there is some parameter and there is some value returning by that function is called Function with return type and with parameter.
#include<stdio.h> int add(int y,int z);//function declaration int add(int y,int z)//function definition { int x; x=y+z; //return value of x return x; } int main() { //assigning return value to variable rs int rs=add(20,30);//function calling printf("Add=%d",rs); } /* ###Output### Add=50 */
In the above example there is two parameter and the function will return integer value because there is int keyword in the place of return type and returned value will assign to variable rs.
Calling of Function
There are two way of calling a function1. Call By Value.
2. Call By Reference.
Call by Value
In this type of calling a function direct value is passed at the time of calling.
In call by value the changes made in formal parameters don't reflect in actual parameters.
#include<stdio.h> void add(int m)//function definition { //adding 10 to m m=m+10; } int main() { int x=10; printf("Before Calling x=%d\n",x); add(x); printf("After Calling x=%d",x); } /* ###Output### Before Calling x=10 After Calling x=10 */
In the above example we can see that direct value is passed at the time of calling.
Here x is actual parameter and m is formal parameter.
Call by Reference
1.In this type of calling a function ,the reference of the value is passed at the time of calling.
2.In call by value the changes made in formal parameters reflect in actual parameters.
3.Reference is also called address.
4.When the address of data is passed at the time of calling so it is necessary to use pointer in the place of parameter.
For better understanding see the example below-
#include<stdio.h> void add(int *m)//function definition { //adding 10 to m *m=*m+10; } int main() { int x=10; printf("Before Calling x=%d\n",x); add(&x); printf("After Calling x=%d",x); } /* ###Output### Before Calling x=10 After Calling x=20 */
To know the difference between call by value and call by reference focus on the output of the program.
Function with default value
In this type of function ,the function contains a number of parameter with some initial value[for example: void sum(int x=10,int y=20)].At the time of calling if there is no value is passed
[for example: sum();] then the default value will be x=10 and y=20,but if value is passed [for example: sum(5,6);] then the value will be x=5 and y=6.
For better understanding see the example below-
#include<stdio.h> void sum(int x=10,int y=20)//function definition { int result=x + y; printf("Add=%d\n",result); } int main() { int x=10,y=20; printf("Without value\n"); sum();//function calling without value printf("With value\n"); sum(5,6);//function calling with value } /* ### Output ### Without value Add=30 With value Add=11 */
Passing Array to Function
In this type of function ,there is an array in the place of parameter [for example:void sum(int ar[5])] and its value is passed at the time of calling.
#include<stdio.h> void sum(int ar[5])//function definition { int s=0; for(int i=0;i<5;i++) //finding the sum s=s+ar[i]; printf("Total sum of element=%d",s); } int main() { int x[5]={10,20,50,40,60}; sum(x);//function calling with array } /* ### Output ### Total sum of element=180 */
In the above example we can see that there is an array ar[5] in place of parameter and there is an other array x[5]={10,20,50,40,60} and it is passed at the time of calling therefor the value of array x will be copied into array ar.
Recursion
The process of calling a function by itself is called Recursion and the function that calls itself is called Recursive Function.
Factorial of any Number using recursionFactorial of 5=5*4*3*2*1
#include<stdio.h> void factorial(int no,int f)//function definition { if(no>=1) { f=f*no; no--; factorial(no,f); } else printf("Factorial =%d",f); } int main() { int n; printf("Enter any number to find factorial\n"); scanf("%d",&n); factorial(n,1);//function calling with array } /* ### Output ### Enter any number to find factorial 6 Factorial =720 */
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