Cses - exponentiation ii

General Questions
#1

#include <bits/stdc++.h>
using namespace std;

using ll = long long;
const ll MOD = 1e9 + 7;

// BeginCodeSnip{Binary Exponentiation}
ll exp(ll x, ll n, ll m) {
assert(n >= 0);
x %= m;
ll res = 1;
while (n > 0) {
if (n % 2 == 1) { // if n is odd
res = res * x % m;
}
x = x * x % m;
n /= 2; // divide by two
}
return res;
}
// EndCodeSnip

int main() {
int test_num;
cin >> test_num;
for (int t = 0; t < test_num; t++) {
ll a, b, c;
cin >> a >> b >> c;

	ll pow_bc = exp(b, c, MOD - 1);
	ll ans = exp(a, pow_bc, MOD);

	cout << ans << '\n';
}

}

Why we are doing MOD - 1 while calculating b^c and
for a^(b^c) Why we are using actual MOD value?

#2

Fermat’s Little Theorem (Modular Arithmetic)