Pointer and Arrays in C

Before you start with Pointer and Arrays in C, learn about these topics in prior:

• Array in C

• Pointer in C

When an array in C language is declared, compiler allocates sufficient memory to contain all its elements. Its base address is also allocated by the compiler.

Declare an array arr,

int arr[5] = { 1, 2, 3, 4, 5 };

Suppose the base address of arr is 1000 and each integer requires two bytes, the five elements will be stored as follows:

Variable arr will give the base address, which is a constant pointer pointing to arr[0]. Hence arr contains the address of arr[0] i.e 1000.

arr has two purpose -

• It is the name of the array
• It acts as a pointer pointing towards the first element in the array.

arr is equal to &arr[0] by default

For better understanding of the declaration and initialization of the pointer - click here. and refer to the program for its implementation.

NOTE:

• You cannot decrement a pointer once incremented. p-- won't work.

Pointer to Array in C

Use a pointer to an array, and then use that pointer to access the array elements. For example,

#include<stdio.h>

void main()
{
   int a[3] = {1, 2, 3};
   int *p = a;    
   for (int i = 0; i < 3; i++)
   {
      printf("%d", *p);
      p++;
   }
  return 0;
}
  

1 2 3

Here is the syntax:

*(a+i)  //pointer with an array

The above code is same as:

a[i]

Pointer to Multidimensional Array in C

Let's see how to make a pointer point to a multidimensional array. In a[i][j], a will give the base address of this array, even a + 0 + 0 will also give the base address, that is the address of a[0][0] element.

Here is the syntax:

*(*(a + i) + j)

Pointer and Character strings in C

Pointer is used to create strings. Pointer variables of char type are treated as string.

char *str = "Hello";

The above code creates a string and stores its address in the pointer variable str. The pointer str now points to the first character of the string "Hello".

• The string created using char pointer can be assigned a value at runtime.

char *str;
str = "hello";    

• The content of the string can be printed using printf() and puts().

printf("%s", str);
puts(str);

• str is a pointer to the string and also name of the string. Therefore we do not need to use indirection operator *.

Array of Pointers in C

Pointers are very helpful in handling character arrays with rows of varying lengths.

char *name[3] = { 
    "Adam",
    "chris",
    "Deniel"
};
//without pointer
char name[3][20] = { 
    "Adam",
    "chris",
    "Deniel"
};

In the second approach memory wastage is more, hence it is preferred to use pointer in such cases.

Suggested Tutorials:

• Pointers with Function

• Pointer to Structure

• Pointer Arithmetic

• Pointer to Array Program