Defining a global variable in main ()

Question

I want to define a global array (used in other functions) based on input main (); (specific array size). The extern keyword did not help.

#include <iostream> using namespace std; void gen_sieve_primes(void); int main() { int MaxNum; cin >> MaxNum; int *primes = new int[MaxNum]; delete[] primes; return 0; } //functions where variable MaxNum is used 

Answer 1

You declare it outside the main:

 int maxNum; int main() { ... } 

Ideally, you do not do this at all. Globals are rarely useful, and hardly ever (or rather: never) are needed.

Answer 2

Just define it in a global area

 int MaxNum; int main(){ cin >> MaxNum; } 

Answer 3

Declare an array outside the main functional brackets.

 #include <iostream> using namespace std; void gen_sieve_primes(void); (Declare the variables here!) int main() { extern int MaxNum; cin >> MaxNum; int *primes = new int[MaxNum]; delete[] primes; return 0; } //functions where variable MaxNum is used