Array Sizing

C++:
simple safe solution use std::vector and resize it.
use new to allocate memory when you know the size, don't forget to call delete [] (and dont forget the brackets)

C:
use malloc don't forget to call free when you're done

C99:
use a function having a VLA

C/C++ non portable but supported on most platforms:
_alloca does stack based allocation cleaned up on function exit

Quote:

Original post by Penguinzchaseme and I need to size an integer based on input: int main() { int N; cin >> N; if(N < 1000) long int x; else int x; } but of course that doesn't work, it just give me a "x undeclared" error

There is no real way to do what you're trying to do at runtime. You know integers can hold values in the range [-2,147,483,648, 2,147,483,647]? If you expect the input would be larger than that, consider an unsigned type.

[EDIT] Fixed.

[Edited by - wild_pointer on July 1, 2004 2:51:36 PM]

For the array: See what DigitalDelusion said.

For the type switch: No can do at run time. And anyway, you do realize that on todays computers, you generally have sizeof(long) == sizeof(int), right?

Quote:

Original post by wild_pointer There is no real way to do what you're trying to do at runtime. You know integers can hold values in the range [-32,767, 32,767]? If you expect the input would be larger than that, just use a long (or unsigned data type if you're unworried about negative values).

Errm, correct me if I'm wrong, but haven't most of us switched to 32 bit systems, with 32 bit ints a decade or so ago? ;)

Quote:

Original post by Spoonster Quote: Original post by wild_pointer There is no real way to do what you're trying to do at runtime. You know integers can hold values in the range [-32,767, 32,767]? If you expect the input would be larger than that, just use a long (or unsigned data type if you're unworried about negative values). Errm, correct me if I'm wrong, but haven't most of us switched to 32 bit systems, with 32 bit ints a decade or so ago? ;)

Yes, I'm retarded. And even shorts are [-32,768, 32,767].

Hey thanks everyone I think I'm going to try something with unsigned and if that doens't work than I'll switch to a vector.

Quote:

Original post by Fruny For the array: See what DigitalDelusion said. For the type switch: No can do at run time. And anyway, you do realize that on todays computers, you generally have sizeof(long) == sizeof(int), right?

On the other hand, with 64-bit CPU's slowly gaining a foothold, this may not hold true much longer. On the AMD64 platform, sizeof(int) == 4 while sizeof(long) == 8; I don't recall what, say, PPC64 does, but I would not be surprised to find something extremely similar.

Of course, why one would do such a thing as the OP suggests in the first place is a bit unclear to me.