Difference between *ptr += 1 and * ptr ++ in C

In C, *ptr += 1 and *ptr++ appear similar at first glance, but they have critical differences. Let's break down these expressions step by step:

*ptr += 1

This operation can be broken down into two steps:

1. Dereference the pointer ptr to obtain its value.
2. Increment this value by 1.

Overall, *ptr += 1 is equivalent to *ptr = *ptr + 1. This means you modify the value at the memory location pointed to by ptr without altering the pointer's address.

*ptr++

This operation can also be broken down into two steps, but with a subtle distinction:

1. Dereference the pointer ptr to obtain its value (access this value).
2. Then increment the pointer ptr itself, so that it points to the next element's location (typically the next memory address, depending on the data type's size).

It is important to note that ptr++ uses the post-increment operator, meaning the increment occurs after the value is accessed. Therefore, *ptr++ effectively accesses the current value and then advances the pointer to the next position.

Practical Example

Assume we have an integer array int arr[] = {10, 20, 30}; and a pointer int *ptr = arr; pointing to the first element.

• If we execute *ptr += 1;, then arr becomes {11, 20, 30}, and ptr still points to arr[0].
• If we execute *ptr++;, then ptr now points to arr[1] (value 20). The array arr remains unchanged, still {10, 20, 30}.

Summary

In summary, *ptr += 1 modifies the current value pointed to by the pointer, while *ptr++ accesses the current value and then moves the pointer. These operations are crucial when working with arrays and pointer arithmetic, as they enable efficient data processing or iteration. In practical programming, selecting the correct operation prevents errors and optimizes code logic.