How to Fix the \"Expected Constant Expression\" Error When Declaring Arrays in C ?

Resolving "Expected Constant Expression" Error for Array Size

Consider the following C code:

<code class="cpp">int count = 0;
float sum = 0;
float maximum = -1000000;

std::ifstream points;

int size = 100;
float x[size][2]; // <<< Error

This code raises an "expected constant expression" error when declaring the array x. This error occurs because C requires non-static array sizes to be known at compile time.

Solution Using Vectors

To resolve this issue, we can use a C vector instead of an array:

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

Solution Using new

Another approach involves dynamically allocating the array using the new operator:

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

Alternative Solutions

• Use Boost: If you have access to the Boost library, you can use boost::array instead of std::array.
• Define Custom Array Type: Define a custom array type that supports dynamic sizing and use it in a vector.

Considerations for Non-C 11 Compilers

If you don't have C 11 support, use the following techniques:

• Use an identity template to simplify the syntax when using new.
• Use a vector of std::pair as an alternative to the vector solution mentioned earlier.

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