Array[n] vs Array[10] - Initializing array with variable vs real number
Solution 1:
In C++, variable length arrays are not legal. G++ allows this as an "extension" (because C allows it), so in G++ (without being -pedantic
about following the C++ standard), you can do:
int n = 10;
double a[n]; // Legal in g++ (with extensions), illegal in proper C++
If you want a "variable length array" (better called a "dynamically sized array" in C++, since proper variable length arrays aren't allowed), you either have to dynamically allocate memory yourself:
int n = 10;
double* a = new double[n]; // Don't forget to delete [] a; when you're done!
Or, better yet, use a standard container:
int n = 10;
std::vector<double> a(n); // Don't forget to #include <vector>
If you still want a proper array, you can use a constant, not a variable, when creating it:
const int n = 10;
double a[n]; // now valid, since n isn't a variable (it's a compile time constant)
Similarly, if you want to get the size from a function in C++11, you can use a constexpr
:
constexpr int n()
{
return 10;
}
double a[n()]; // n() is a compile time constant expression