Why Does My C Array Declaration Produce the 'expression must have a constant value' Error?

Unveiling the Enigma: Deciphering "Expression Must Have a Constant Value" in C Array Declarations

When encountering the enigmatic error message "expression must have a constant value" while attempting to declare an array in C , it's imperative to delve into the intricacies of array initialization.

The error arises when the size of an array is designated using variables, as in the example you provided:

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

In this instance, the issue stems from the array's size being dictated by variables. For an array declaration to succeed, its dimensions must be constant, meaning firmly established at compile time. However, when variables are involved, their values are subject to change during program execution, rendering an array's size fluid and variable.

To resolve this quandary, two viable solutions emerge:

1. Dynamic Memory Allocation:

If you desire an array with a size that can fluctuate during program execution, you can harness the power of dynamic memory allocation on the heap. This involves explicitly allocating memory for the array at runtime with the new operator and subsequently deallocating it with the delete operator when it's no longer needed.

// 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;

2. Constant Declarations:

Alternatively, if a fixed-size array is your objective, you can declare the array dimensions as const, indicating that their values will remain unwavering throughout the program's lifetime.

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

In conclusion, when encountering the "expression must have a constant value" error in C array declarations, the key lies in ensuring the array's dimensions are constant at compile time. By employing either dynamic memory allocation or constant declarations, you can effortlessly navigate this hurdle and harness the power of arrays in your coding endeavors.

The above is the detailed content of Why Does My C Array Declaration Produce the 'expression must have a constant value' Error?. For more information, please follow other related articles on the PHP Chinese website!