Pointer Arithmetics in C with Examples
Pointers variables are also known as address data types because they are used to store the address of another variable. The address is the memory location that is assigned to the variable. It doesn’t store any value.
Hence, there are only a few operations that are allowed to perform on Pointers in C language. The operations are slightly different from the ones that we generally use for mathematical calculations. The operations are:
- Increment/Decrement of a Pointer
- Addition of integer to a pointer
- Subtraction of integer to a pointer
- Subtracting two pointers of the same type
Increment/Decrement of a Pointer
Increment: It is a condition that also comes under addition. When a pointer is incremented, it actually increments by the number equal to the size of the data type for which it is a pointer.
If an integer pointer that stores address 1000 is incremented, then it will increment by 2(size of an int) and the new address it will points to 1002. While if a float type pointer is incremented then it will increment by 4(size of a float) and the new address will be 1004.
Decrement: It is a condition that also comes under subtraction. When a pointer is decremented, it actually decrements by the number equal to the size of the data type for which it is a pointer.
If an integer pointer that stores address 1000 is decremented, then it will decrement by 2(size of an int) and the new address it will points to 998. While if a float type pointer is decremented then it will decrement by 4(size of a float) and the new address will be 996.
Below is the program to illustrate pointer increment/decrement:
Pointer ptr1 before Increment: 0x7ffcb19385e4 Pointer ptr1 after Increment: 0x7ffcb19385e8 Pointer ptr1 before Decrement: 0x7ffcb19385e8 Pointer ptr1 after Decrement: 0x7ffcb19385e4
When a pointer is added with a value, the value is first multiplied by the size of data type and then added to the pointer.
Pointer ptr2 before Addition: 0x7fffffdcd984 Pointer ptr2 after Addition: 0x7fffffdcd990
When a pointer is subtracted with a value, the value is first multiplied by the size of the data type and then subtracted from the pointer.
Below is the program to illustrate pointer Subtraction:
Pointer ptr2 before Subtraction: 0x7ffcf1221b24 Pointer ptr2 after Subtraction: 0x7ffcf1221b18
Subtraction of Two Pointers
The subtraction of two pointers is possible only when they have the same data type. The result is generated by calculating the difference between the addresses of the two pointers and calculating how many bits of data it is according to the pointer data type. The subtraction of two pointers gives the increments between the two pointers.
Two integer pointers say ptr1(address:1000) and ptr2(address:1016) are subtracted. The difference between address is 16 bytes. Since the size of int is 2 bytes, therefore the increment between ptr1 and ptr2 is given by (16/2) = 8.
Below is the implementation to illustrate the Subtraction of Two Pointers:
Subtraction of ptr1 & ptr2 is 3
Pointer Arithmetic on Arrays:
Pointers contain addresses. Adding two addresses makes no sense because there is no idea what it would point to. Subtracting two addresses lets you compute the offset between the two addresses. An array name acts like a pointer constant. The value of this pointer constant is the address of the first element. For Example: if an array named arr then arr and &arr can be used to reference array as a pointer.
Below is the program to illustrate the Pointer Arithmetic on arrays:
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