Error expression must have a constant value in C++ length occurs when you try to use a non-constant value in a context that requires a constant expression.
To fix the error in C++, use a constant size for arrays or replace the array with a dynamically sized container like std::vector.
Reproducing the error
cin >> n;
expression must have a constant value in C++ length
How to fix it?
Here are three ways to fix this error programmatically:
- Use a constant expression for array size
- Use dynamic allocation
- Use a standard library container
Solution 1: Use a constant expression for array size
If the size can be determined at compile time, define it as a constant.
const int SIZE = 10;
Solution 2: Use dynamic allocation
If the size is known only at runtime, use dynamic memory allocation:
int* array = new int[n];
// Remember to delete the array after use
Solution 3: Use a standard library container
A more modern and safer approach is to use a standard library container like std::vector, which handles dynamic sizing.