Functions

Functions

AU: Dec.-18, May-19, Marks 13

If certain set of instructions is required frequently then those instructions are wrapped within a function.

C programmer handles the C function using three methods -

1. Declaration of function

2. Definition of function

3. Call to the function

For example

void main( )

{

void sum( ); /* declaration of the function*/

sum( ); /*call to the function*/

}

void sum( ) /*definition of the function*/

}

int a,b,c;

printf("\n Enter The two numbers");

scanf("%d %d",&a,&b);

c=a+b;

printf("\n The Additon Of two numbers is %d",c);

}

The syntax for declaration of the function is

Return_type Function_name(Data_type Parameter);

The syntax for definition of the function is

Return_type Function_name(Data_type Parameter)

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{

//body of function

}

The syntax for call to the function is

Function_name(Parameters);

 

1. Parameter Passing Method

Type 1. Passing nothing and returning nothing.

void main( )

{

void sum ( ); /*declaration of the function*/

}

void sum( ) /*definition of the function*/

{

int a,b,c;

printf("\n Enter The two numbers");

scanf("%d %d",&a,&b);

c=a+b;

printf("\n The Additon Of two numbers is %d",c);

}

In above example no parameter is passed and there is no return value from the function. Hence the data type of the above function is void. The void data indicates that the function is returning nothing or returning NULL.

We can also pass the argument as void to the function main. The parameter void to function main indicates that there are no parameters to the function main. Thus instead of void main() we can write void main(void)

 

Ex. 1.8.1 Write use of void data.

Solution :

• The void data type indicates that the function is returning nothing.

• If the function is not returning anything from the function then its data type is specified as void. We can also pass the argument void to the function to indicate that there are no parameters to the function.

Type 2. Passing the parameter and returning nothing.

Here we will see a sample C code in which the function is written with some parameter.

main( )

{

int a,b;

void sum(int a,int b);/*declaration*/

printf("\n Enter The two numbers");

scanf("%d",&a,&b);

sum(a,b);/*call*/

}

void sum(int x, int y)/*definition*/

{.

int c;

c=x+y;

printf("\n The Addition is %d",c);

}

The parameters a and b are passed. In the definition we have interpreted them as x and y. You can take them as a, b respectively or x, y or any other names of your own choice. It makes no difference. It takes them as a and b only. There are actually two methods of parameter passing.

1. Call by Value.

The above example which we have discussed is of parameter passing by call by value. This is called by value because the values are passed.

2. Call by Reference.

In call by reference the parameters are taken by reference. Pointer variables are passed as, parameters.

For example

main()

{

int a,b;

void sum(int *,int *);

printf("\n Enter The Two Numbers");

scanf("%d %d",&a,&b);

sum(&a,&b);

}

void sum(int *x,int *y)

{

int c;

c=*x+*y;

printf("%d",c);

}

Difference between Call by Value and Call by Reference

Type 3.

Passing the parameters and returning from the function

In this method the parameters are passed to the function. And this function returns some value. If the function is returning integer value then the data type of that function is int. Thus depending upon the type of data which is returning from the function the data type of that function is determined. If nothing is returned form the function then that function has a void data type.

void main( )

{

int a,b,c;

int sum(int,int);/* Only mentioning of data type is allowed

for the parameters*/

printf("\n Enter The Two Numbers");

scanf("%d %d",&a,&b);

c = sum(a,b);

printf("\n The Addition Is =%d",c);

}

int sum()

{

c = a+b;

return c; /*returning c which is of int type*/

/*so data type of sum is int*/

}

 

Ex. 1.8.2 Write a C program to interchange two variables without using third variable.

Solution :

/**************************************

Program to interchange two variables without using third variable

***************************************/

#include <stdio.h>

void main( )

{

int a=11;

int b=20;

printf("\na= %d b=%d",a,b);

a = a+b;

b = a-b;

a = a-b;

printf("\na= %d b=%d",a,b);

}

 

Ex. 1.8.3: Write a C program to get two numbers and exchange these numbers using pass by value and pass by reference. AU: Dec.-18, Marks 7

Sol.:

#include<stdio.h>

void swap_by_value(int a, int b)

{

int temp;

temp = a;

a = b;

b = temp;

}

void swap_by_ref(int *a, int *b)

{

int temp;

temp = *a

*a = *b;

*b= temp;

}

int main( )

{

int x, y;

printf("\nEnter First number: ");

scanf("%d", &x);

 

printf("\nEnter Second number: ");

scanf("%d", &y);

 

printf("\nBefore Swaping x = %d and y = %d", x, y);

swap_by_value(x,y); // Function Call - Pass By Value

printf("\nAfter Swaping(By Value) x = %d and

y = %d", x, y);

printf("\nBefore Swaping x = %d and y = %d", x, y);

swap_by_ref(&x,&y); // Function Call - Pass By Reference

printf("\nAfter Swaping (By Reference) x = %d and

y = %d", x, y);

}

Output

Enter First number: 10

Enter Second number: 20

Before Swaping x = 10 and y = 20

After Swaping (By Value) x = 10 and y = 20

Before Swaping x = 10 and y = 20

After Swaping (By Reference) x = 20 and y = 10

Review Questions

1. Explain with a suitable example, function call by reference and function call by value.

2. Write suitable 'C' program that creates different results after passing a parameter by reference and by values.

3. Illustrate pass by value and pass by reference in functions with an example.

AU May-19, Marks 13