Question

I try to create series of multidimensional arrays with for loops. User should input the number of arrays to be initialized. I want something like this:

int i;
printf("Enter the number of arrays you want: ");
scanf("%d",i)
for(int j=0;j<i;j++){
     long double x(j)[size][size];
}

if I input 5, I want to have x0, x1, x2, x3 and x4.

Is it possible at all??

Thank you for any help.

Best Regards,
Emre.

Answer 1

Edit: Just noticed you are using C++. In this case, std::vector is definitely the most convenient solution. If you are curious about how to do this with plain arrays, C style, then read on…

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You can’t do it like this. What you need to do is create a 3 dimensional array (or an array of 2-dimensional arrays, depending on your point of view…)

As is always the case with C, memory allocation is a pain… You can statically allocate:

long double x[N][size][size];

(N is determined at compile time. Make sure you have it large enough.
Also if N is really big, declare the array stactically (either as a global variable or with the static keyword). If you don’t you can get a stack-overflow.)

Or you can use dynamic memory allocation:

long double (*x)[size][size]; // x is a pointer to size by size arrays
x = malloc(n * sizeof(*x));
//You can now use x[j][a][b]...

Maybe things look better with a typedef (even I am not 100% sure I got that array ceclaration right in the last example…):

typedef long double typename_here[size][size];
typename_here *x;
x = malloc(n * sizeof(typename_here);

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BTW, the reason your current code doesn’t work is

1. The x(j) syntax is ficticious 🙂
2. Variables declared inside a loop are internal to that block. This means you can’t access them after the loop body.