Function
Function
Function is set of instructions to carry out a particular task.
A C program has at least one function main( ). Without main() function, there is technically no C program.
A function can be called multiple times to provide reusability and modularity to the C program. In other words, we can say that the collection of functions creates a program. The function is also known as procedureor subroutinein other programming languages.
Why we use function in C programming?
- It is very difficult for the programmer to write large programs.
- Very difficult to identify the logical errors and correct.
- Very difficult to read and understand.
- Large programs are more complex to find the errors.
To overcome all the difficulties we use Function in C programming.
Tyes of function in C
There are two types of functions in C on basis of whether it is defined by user or not.
- Library Function
- User defined Function
1)Library Function
Library functions are the pre-defined function in C programming language.
1.main()
- The execution of every C program starts from this main() function.
- If you want to use printf and scanf function, the header file <stdio.h> should be included.
2.printf()function
- prinf() is used for displaying output in C.
3.scanf() function
- scanf() is used for taking input from user in C.
There are many library functions available in C programming to help the programmer to write a good efficient program.
In C programming you can copy string by just using strcpy() function which is defined under header file
"string.h".
These are some other library functions defined in "string.h"
- strcmp();
- strcat();
- strlen(); etc.
2)User defined Functions
C provides programmer to define their own function according to their requirement is known as "user defined functions".
Advantages of user defined functions
- User defined functions helps to reduce the large program into small segments which makes programmer easy to understand, maintain and debug.
- If repeated code occurs in a program. Function can be used to include those codes and execute when needed by calling that function.
- Programmer working on large project can divide the workload into some function by making different functions.
Elements of user defined functions:
- Function declaration
- Function call
- Function definition
1.Function declaration
Syntax:
Funtion_type function_name(parameter list);
A function declaration consists of four parts. They are,
- Function type
- Function name
- Parameter list
- Terminating semicolon
Example:
int add(int a, int b);
2.Function call
Invoking(calling) of a function is called "function call".
Syntax:
function_name(Parameter name);
Example:
add(a,b);
3.Function definition
The program module that is written to achieve a specific task is called "function definition".
Syntax:
Function Type Function name (Parameter List)
{
Local declaration;
Function statements;
Return statements;
}
Function Header
The function header consists of three parts:
function type,
function name
list of
parameter.
- Function type
- Function name
- List of parameters
The function type specifies the type of value (like int or float) that the function is expected to return to the calling program. If the return type is not specified then C will assume that it is an integer type(int).
The function name is any valid C identifier and the name should be appropriate to the task performed by the function.
The parameter list declares the variables. In this variables will store the received data sent by the calling program. They serve as input data to the function to carry out the specific task.
Example:
1) Float sub (float x, float y)
2) int mul (int a, int b)
Function body
Function body is inside the curly braces. It contain Following three parts :
- Function variable declaration
- Function statement
- Return statement
It is a statement that specify the variables.
It is a statement that perform the task of the function.
It is a statement that returns the value evaluated by the function.
Syntax with Example:
int add(int a, int b)
{
int sum;
sum=a+b;
return sum;
}
Sample program
Addition of two integer numbers using user defined function.
#include<stdio.h>
#include<conio.h>
//Function declaration
int sum(int a, int b);
void main()
{
int a,b,x;
clrscr();
printf("Enter any two number of type integer/n");
scanf("%d%d"&a,&b);
// Function call
x=sum(a,b);
printf("Sum of two numbers=%d",x);
getch();
}
// Function Definition
int sum(int a, int b)
{
int sum;
sum=a+b;
return(sum);
}
Output-
Enter any two number of type integer
10
11
Sum of two numbers=21
Functions Prototypes (Function Declaration)
On the basis of parameters and return values, the functions declaration classified into following types-
- Function with no return type and no arguments.
- Function with return type but with no arguments.
- Function with no return type but with arguments.
- Function with return type and with arguments.
1.Function with no return type and no arguments.
In this method, there is no data transfer between the calling function and called function.Return type is void. So this returns nothing.
Sample program
Swap two numbers using user defined function with no argument and no return type
#include<stdio.h>
#include<conio.h>
void swap();
void main()
{
clrscr();
swap();
getch();
}
void swap()
{
int num1.num2,temp;
num1=10;
num2=11;
temp=num1;
num1=num2;
num2=temp;
printf("num1=%d" and num2=%d,num1,num2);
}
Output-
num1=11 and num2-10
2.Function with return type but with no arguments.
In this method, there is no data transfer between the calling function and called function.Here we won’t pass any arguments to the function while defining, declaring or calling the function.
Sample program
Implement a program to find maximum of two numbers using function (Prototype: no argument, with return type)
#include<stdio.h>
#include<conio.h>
int max();
void main()
{
int y;
clrscr();
y=max();
printf("max=%d",y);
getch();
}
int max()
{
int a,b;
printf("Enter any two numbers\n");
scanf("%d%d",&a,&b);
if(a>b)
{
return(a);
}
else
{
return(b);
}
}
Output-
Enter any two numbers
10
11
max=11
3.Function with no return type but with arguments.
In this method, we pass the arguments to the function while calling the function. But, This type of function will not return any value when we call the function from main() function.
Sample program
Implement a program to find minimum of number using function (Prototype: with argument, no return type)
#include<stdio.h>
#include<conio.h>
void min(int a,int b);
void main()
{
int a,b;
clrscr();
printf("Enter any two numbers");
scanf("%d%d",&a,&b);
min(a,b);
getch();
}
void min(int a,int b)
{
if(a < b)
{
printf("%d is minimum",a);
}
else
{
printf("%d is minimum",b);
}
}
Output-
Enter any two numbers
10
11
10 is minimum
4.Function with return type and with arguments.
In this method, it allows us to pass the arguments to the function while calling the function. This type of function will return some value when we call the function from main() function.
Sample program
Implement a program to find average of three numbers using function (Prototype: with argument, with return type)
#include<stdio.h>
#include<conio.h>
int avg(int a,int b,int c);
void main()
{
int a,b,c,A;
clrscr();
printf("enter three numbers\n");
scanf("%d%d%d",&a,&b,&c);
A=avg(a,b,c);
printf("average=%d",A);
getch();
}
int avg(int a,int b,int c)
{
int average;
average=(a+b+c)/3;
return(average);
}
Output-
enter three numbers
11
10
9
average=10
Methods of parameter(Argument) passing
- Pass by value(call by value)
- Pass by address (call by address)
1.Pass by value(call by value)
In this method, the value of the actual parameters is copied into the formal parameters.
The actual parameter is the argument used in the function call whereas and parameter is the argument which
is used in the function definition. Here we can't modify the value of the actual parameter by the formal
parameter.
By default, C programming uses call by value to pass arguments.
Sample program
#include<stdio.h>
int sum(int a, int b)
{
int c=a+b;
return c;
}
int main(
{
int var1 =10;
int var2 = 20;
int var3 = sum(var1, var2);
printf("sum=%d", var3);
return 0;
}
Output-
sum=30
2.Pass by address (call by address)
[We will learn this concept in pointer tutorial.]
Examples For Practice
- Implement a program to find maximum of two numbers using function (Prototype: no argument, no return type)
- Find Factorial of any number using user defined function.
- Find whether given number is Armstrong number or not using user defined function Armstrong Number: If the number is equal to sum of cube of each digits in number.