\"Why Does Declaring an Array with a Runtime-Determined Size Cause an \"Expected Constant Expression\" Error?\"

Error: "Expected Constant Expression" for Array Size

When attempting to declare an array with a runtime-determined size, as in the following code snippet:

<code class="cpp">int size = 100;
float x[size][2];</code>

you may encounter the error "expected constant expression." This error occurs because declared arrays must have their size determined at compile time.

Solution: Use a Vector or Dynamic Array Allocation

To resolve this issue, consider using a vector or dynamic array allocation. Using a vector, you can specify the size at runtime:

<code class="cpp">std::vector< std::array<float, 2> > x(size);</code>

Alternatively, you can use the new operator to dynamically allocate the array:

<code class="cpp">float (*px)[2] = new float[size][2];</code>

Other Options:

• Boost Array: If you do not have C 11, use Boost library's boost::array.
• Custom Array Type: Create a custom array type that can be placed in a vector.
• Identity Template: Simplify syntax for dynamic array allocation using an identity template.
• Vector of Pairs: Use a vector of std::pair to store the data.

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