variable undeclared (first use in this funcion)

Code:

---

#include <iostream>
#include <fstream>

using namespace std;

int prime [10000];
int index = 0, min, max;

bool isPrime(int x);
void genPal(int num, int add, int mulleft, int mulright);

int main(){
        ifstream fin ("pprime.in");
        ofstream fout ("pprime.out");
        fin >> min >> max;
        int max2 = max;
        int length;
        for(length = 0; max2; length++){
                max2 /= 10;
        }
        cout << length << '\n';
}

bool isPrime(int x){
        if(x < min || x > max || x%2 == 0 || x%3 == 0)
                return false;
        for(int i = 2; i*i < x; i++)
                if(x%i == 0)
                        return 0;
        return true;
}

void genPal(int num, int add, int mulleft, int mulright){
        int i, nmulleft, nmulright;
        if(num == 2)
                for(i = 0; i < 10; i++)
                        add+mulleft * i + mulright * i << '\n';
        else if(num == 1)
                for(i = 0; i < 10; i++)
                        cout << add + mulright * i << '\n';
        else{
                nmulleft = mulleft / 10;
                nmulright = mulright * 10;
                num -= 2;
                for(i = 0; i < 10; i++)
                        genPal(num, add+i*mulleft + i*mulright, nmulleft, nmulright);
        }
}

---

The errors:
test.cpp: In function 'int main()':
test.cpp:15: error 'min' undeclared(first use in this function)
and others like this. How do I fix this without making the variable min local to the main method?

It is a bad idea to use variables named min and max, especially with the using directive using namespace std, due to possible conflicts with std::min and std::max (and then possible conflicts with certain Windows specific macros named min and max).

Incidentally, you should avoid the use of global variables, though in this case a global array of primes is arguably tolerable. The min and max global variables, on the other hand, are not so tolerable, and index is not even used.