Pointers

Pointers

• Pointer is a variable in which we can store memory address of other variable.
• If a pointer contains address of variable in it then it means that pointer is pointing to that variable.
• If a pointer is pointing to a variable then by using such pointer we can access that variable.

Defining a Pointer

• A pointer is a variable where we can store address of a variable.
• Pointer can be defined by using indirection operator '*'.
• It will create a pointer variable in which we can store address of variable of specified type.

• int *p;
• float *q;
• char *s;

AddressOf Operator (&)

• A pointer is a variable where we can store address of a variable.
• Address of a variable can be find out by using addressof operator (&) which we can store into a pointer variable.

• int a=5,*p; //it will create a variable a and a pointer p
• p=&a; //it will store address of a into pointer p

Indirection Operator(*)

• If a pointer contains address of a variable in it then it means that the pointer is pointing to that variable.
• If a pointer is pointing to a variable then by using such pointer variable we can be access that variable with the help of indirection operator (*).

• int a=5,*p; //it will create a variable a and a pointer p
• p=&a; //it will store address of a into pointer p
• printf("%d",a); // will print value of a
• printf("%d",*p); // will print value of a as pointer p is pointing to it

Pointer Arithmetic

• We can perform different arithmetic operations and comparison operations on the pointer variable.
• The Arithmetic operators behaves differently with pointers. The result of expression depends on data type of pointer(i.e. size of data type)
• Following arithmetic and comparison operations are possible on pointer:
• Increment + +
• Decrement - -
• Addition +
• Subtraction -
• Comparison < > <= >= == !=

• We can subtract two pointers. This is because difference between two pointers gives the number of elements of its data type that can be stored between the two pointers.
• We cannot add two pointers. This is because pointers contain addresses, adding two addresses makes no sense, because you have no idea what it would point to.

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

5 5 5
8 8 8
  

  #include<stdio.h>
  main()
  {
    int a=5,b=10,*p,*q;
    p=&a;
    q=&b;
    printf("\n%d %d %d %d",a,b,*p,*q);
    (*p)++;
    (*q)--;
    printf("\n%d %d %d %d",a,b,*p,*q);
    *p=*p+5;
    *q=*q-5;
    printf("\n%d %d %d %d",a,b,*p,*q);
  }

5 10 5 10
6 9 6 9
11 4 11 4
  

  #include<stdio.h>
  main()
  {
    int a=5,b=10,*p,*q;
    p=&a;
    q=&b;
    printf("\n%d %d %d %d",a,b,*p,*q);
    a=b;
    (*p)++;
    (*q)--;
    printf("\n%d %d %d %d",a,b,*p,*q);
    *p=*q;
    (*p)++;
    (*q)--;
    printf("\n%d %d %d %d",a,b,*p,*q);
  }

5 10 5 10
11 9 11 9
10 8 10 8
  

  #include<stdio.h>
  main()
  {
    int a=5,b=10,*p,*q;
    p=&a;
    q=&b;
    printf("\n%d %d %d %d",a,b,*p,*q);
    *p=*q;
    *p=*p+*q;
    *q=*p-*q;
    printf("\n%d %d %d %d",a,b,*p,*q);
    p=q;
    (*p)++;
    (*q)--;
    printf("\n%d %d %d %d",a,b,*p,*q);
  }

5 10 5 10
20 10 20 10
20 10 10 10
  

  #include<stdio.h>
  main()
  {
    float a [5]={1.2,4.8,3.6,7.1,0.2};
    float *p;
    p=a; 
    printf("Result is %f\n",a[2]);
    printf("Result is %f\n",2[a]);
    printf("Result is %f\n",*(p+2));
    printf("Result is %f\n",*(a+2));
  }

Result is 3.600000
Result is 3.600000
Result is 3.600000
Result is 3.600000