Why Can't I Initialize a C Array with a Variable Length?

Understanding Array Initialization with Variable vs. Numeric Literals

Problem:

In C , attempting to initialize an array with a variable length, such as int n = 10; double tenorData[n] = {1, 2, 3, ...}, results in a compilation error. However, initializing with a fixed length, like double tenorData[10], succeeds. Why does this occur?

Answer:

In C , variable-sized arrays are not permissible. While extensions in certain compilers (e.g., G ) allow them, they remain illegal according to the standard. To create arrays with variable lengths in C , you can either:

• Dynamically allocate memory: Allocate memory manually using pointers, but remember to deallocate it later.
• Use standard containers: Utilize containers like std::vector to handle dynamic memory management.

If you still require an array, consider using a constant value instead of a variable:

• Constant: Declare the array size as a constant, such as const int n = 10; double a[n];, as constants are evaluated at compile time.
• Constexpr (C 11 ): For values determined by functions, employ constexpr, which also evaluates expressions at compile time.

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