为什么有很多人都要用函数，明明这样也行啊？

#include<bits/stdc++.h>

using namespace std;
int b[10000], c;

int main() {
    int n;
    cin >> n;
    for (int i = 2; i <= n; i++) {
        int a = 0;
        for (int j = 2; j <= sqrt(i); j++) {
            if (i % j == 0) {
                a = 1;
            }
        }
        if (a == 0) {
            b[i] = 1;
            c = i;
        }
    }
    for (int i = 3; i <= c; i++) {
        if (b[i] == 1 && b[i + 2] == 1) {
            cout << i << ' ' << i + 2 << "\n";
        }
    }
    return 0;
}