Prerequisite : Pointers in C/C++
Consider int arr. The answer lies in the fact how the compiler interprets arr[i] ( 0<=i<100).
arr[i] is interpreted as *(arr + i). Now, arr is the address of array or address of 0th index element of array. So, address of next element in array is arr + 1 (because elements in array are stored in consecutive memory locations), further address of next location is arr + 2 and so on . Going with above arguments, arr + i means address at i distance away from starting element of array. Therefore, going by this definition, i will be zero for starting element of array because starting element is at 0 distance away from starting element of array. To fit this definition of arr[i], indexing of array starts from 0.
The conclusion is, we need random access in array. To provide random access, compilers use pointer arithmetic to reach i-th element.
- Rearrange array such that even index elements are smaller and odd index elements are greater
- Longest alternating sub-array starting from every index in a Binary Array
- Construct an array from XOR of all elements of array except element at same index
- Sum of the elements from index L to R in an array when arr[i] = i * (-1)^i
- Equilibrium index of an array
- Find the index of first 1 in a sorted array of 0's and 1's
- Sort the array in a given index range
- Array Index with same count of even or odd numbers on both sides
- Delete array element in given index range [L - R]
- Find the index of first 1 in an infinite sorted array of 0s and 1s
- Overloading Subscript or array index operator  in C++
- Index with Minimum sum of prefix and suffix sums in an Array
- Find the index of the left pointer after possible moves in the array
- Find a Fixed Point (Value equal to index) in a given array
- Count of index pairs with equal elements in an array
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