「SuperOJ 214」三角形面积

#include <bits/stdc++.h>
using namespace std;
float a, b, c;
inline bool check() {
    if (a + b > c && fabs(a - b) < c) return true;
    return false;
}
int main() {
    ios::sync_with_stdio(false);
    cin.tie(NULL);
    cin >> a >> b >> c;
    if (!check())
        cout << "No.", exit(0);
    else {
        register int p = (a + b + c) / 2;
        cout << fixed << setprecision(2)
             << sqrt(p * (p - a) * (p - b) * (p - c));
    }
    return 0;
}