字符串查询函数 find()

#include <iostream>
#include <cmath>

using namespace std;

int main() {
	int n; cin >> n;
	string B = "0123456789ABCDEF";
	for (int i = 0; i < n; i++) {
		string s; cin >> s;
		bool b2 = true;
		bool b8 = true;
		bool b10 = true;
		bool b16 = true;
		for (char c: s) {
			size_t p = B.find(c); // 查找是否在
			if (p == string::npos) {
					b2 = b8 = b10 = b16 = false;
					break;
			}
			if (p > 1) b2 = false;
			if (p > 7) b8 = false;
			if (p > 9) b10 = false;
		}
		cout << b2 << ' ' << b8 << ' ' << b10 << ' ' << b16 << endl;
	}
}

解析：找出每个字符串中最大的字符，根据其大小判断可能是几进制数，详见代码：

#include <iostream>
using namespace std;
int main() {
    int n = 0;
    cin >> n;
    for (int i = 0; i < n; i++) {
        string s;
        cin >> s;
        char maxc = '0';
        for (int i = 0; i<s.length(); i++)
            if (s[i] > maxc)
                maxc = s[i];
        if (maxc>'F'){
            cout<<"0 0 0 0"<<endl;
        }else if(maxc>'9'){
            cout<<"0 0 0 1"<<endl;
        }else if (maxc>'7'){
            cout<<"0 0 1 1"<<endl;
        }else if (maxc>'1'){
            cout<<"0 1 1 1"<<endl;
        }else{
            cout<<"1 1 1 1"<<endl;
        }
    }
    return 0;
}

另一种解法：

#include <iostream>
using namespace std;
int main() {
    int n = 0;
    cin >> n;
    for (int i = 0; i < n; i++) {
        char str[11];
        cin >> str;
        char max = '0';
        for (int i = 0; str[i] != '\0'; i++)
            if (str[i] > max)
                max = str[i];
        cout << (max <= '1') << " " << (max <= '7') << " " << (max <= '9') << " " <<
             (max <= 'F') << endl;
    }
    return 0;
}

#include <iostream>
#include <string>
using namespace std;
// 二进制
bool is_bin(string n) {
    for (int i = 0; i < n.length(); i++) {
        if (n[i] < '0' || n[i] > '1') return false;
    }
    return true;
}
// 八进制
bool is_oct(string n) {
    for (int i = 0; i < n.length(); i++) {
        if (n[i] < '0' || n[i] > '7') return false;
    }
    return true;
}
// 10 进制
bool is_dec(string n) {
    for (int i = 0; i < n.length(); i++) {
        if (n[i] < '0' || n[i] > '9') return false;
    }
    return true;
}
// 16进制
bool is_hex(string n) {
    for (int i = 0; i < n.length(); i++) {
        if (n[i] > '9' && n[i] < 'A' || n[i] < '0' || n[i] > 'F') return false;
    }
    return true;
}
int main() {
    int k;
    cin >> k;
    for (int i = 0; i < k; i++) {
        string str;
        cin >> str;
        if (is_bin(str)) {
            cout << 1 << " " << 1 << " " << 1 << " " << 1 << endl;
        } else if (is_oct(str)) {
            cout << 0 << " " << 1 << " " << 1 << " " << 1 << endl;
        } else if (is_dec(str)) {
            cout << 0 << " " << 0 << " " << 1 << " " << 1 << endl;
        } else if (is_hex(str)) {
            cout << 0 << " " << 0 << " " << 0 << " " << 1 << endl;
        } else {
            cout << 0 << " " << 0 << " " << 0 << " " << 0 << endl;
        }
    }
    return 0;
}