Why Does C Require Constant Array Sizes: 'Expression Must Have a Constant Value'?

Array Size Must Be Constant: "Expression must have a constant value"

When initializing arrays in C , the array size must be known at compile time. This means that the values for the row and column dimensions of the array must be constant expressions.

Consider the following example:

int row = 8;
int col = 8;
int [row][col]; // error: expression must have a constant value

In this code, the array is declared without specifying a variable name. Additionally, the row and col variables are not constants, so the compiler cannot determine the size of the array at compile time. This results in the "expression must have a constant value" error.

Dynamically Allocated Array

To create a dynamically sized array, memory must be allocated on the heap using new operator. The allocated memory must be deallocated using delete to prevent memory leaks.

// Allocate the array
int** arr = new int*[row];
for (int i = 0; i < row; i++)
    arr[i] = new int[col];

// Use the array

// Deallocate the array
for (int i = 0; i < row; i++)
    delete[] arr[i];
delete[] arr;

Fixed-Size Array

For fixed-size arrays, the row and col dimensions must be declared as const:

const int row = 8;
const int col = 8;
int arr[row][col];

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