Pointers

Call By Value

• If a function is call by passing variable then actually value of that variable is passed as argument to the function.
• Such a function call is called as call by value.
• In this case function receives value of variable (i.e. copy of variable data) as argument.
• So the operations performed by that function on that value are not reflected back on original variable.

  #include<stdio.h>
  void change(int a)
  {
    a++;
  }
  void main()
  {
    int a=5;
    printf("\n%d",a);
    change(a);
    printf("\n%d",a);
  }

5
5
  

Call By Reference

• If a function is call by passing address of variable then such a function call is called as call by reference.
• In this case function receives address of variable as argument.
• Due to this the function can access original variable by using that address.
• So the operations performed by that function by using that address are actually performed on original variable.

  #include<stdio.h>
  void change(int *p)
  {
    (*p)++;
  }
  void main()
  {
    int a=5;
    printf("\n%d",a);
    change(&a);
    printf("\n%d",a);
  }

5
6
  

  #include<stdio.h>
  void swap(int *p,int *q)
  {
    int temp;
    temp=*p;
    *p=*q;
    *q=temp;
  }
  void main()
  {
    int a=5,b=7;
    printf("\nA=%d B=%d",a,b);
    swap(&a,&b);
    printf("\nA=%d B=%d",a,b);
  }

A=5 B=7
A=7 B=5
  

Function returning multiple values

• A function cannot directly return multiple values by using return statement.
• But this can be achieved by passing addresses of variables to the function in which we want the results.
• The function will calculate the result and will store it at the received address.
• In this way the function can indirectly return multiple values.

  #include<stdio.h>
  void Circle(int r,float *p,float *q)
  {
    *p=3.14*r*r;
    *q=2*3.14*r;
  }
  void main()
  {
    float a,c;
    Circle(1,&a,&c);
    printf("Area is %f \n Circcumference is %f",a,c);
  }

Area is 3.140000
Circcumference is 6.280000
  

  #include<stdio.h>
  void rectangle(int l,int b,int *p,int *q)
  {
    *p=l*b;
    *q=2*(l+b);
  }
  void main()
  {
    int a,p;
    rectangle(5,10,&a,&p);
    printf("Area is %d \nPerimeter is %d",a,p);
  }

Area is 50
Perimeter is 30