#include <iostream>
#include <string>
using namespace std;

int main() {
	string a = "1234", b = "1a2b3c";
	int num = 4321;

	// 1. string -> int
	cout << stoi(a) << "\n";
	// 8진수 1234를 -> 10진수로 변환
	cout << stoi(a,nullptr,8) << "\n";


	// 2. string 문자열에서 숫자만 구분하여 출력
	for (int i = 0; i < b.size(); i++) {
		if (b[i] >= '0' && b[i] <= '9') cout << b[i] - '0';
	}
	cout << "\n";


	// 3. int -> string
	string s = to_string(num);
	string r = "결과 = ";

	r += num;
	cout << r << "\n";

	r = "결과 = ";
	r += s;
	cout << r << "\n";

	return 0;
}

#include <iostream>
#include <cmath>
using namespace std;

int main() {
	int a = 3, n = 4, b = 144;

	cout << a << "의 " << n << "승 = " << pow(a, n) << "\n";

	cout << b << "의 " << "양의 제곱근 = " << sqrt(b) << "\n";

	return 0;
}

#include <iostream>
#include <math.h>
#define N 500
#define N2 199
using namespace std;

bool sosu(int n) {
	int k = (int)sqrt(n);
	for (int i = 2; i <= k; i++) {
		if (n % i == 0) return false;
	}
	return true;
}

int main() {
	bool* b = new bool[N + 1];	// 숫자 A을 배열의 A번에 저장하기 위하여 크기 N+1
	for (int i = 2; i < N+1; i++) b[i] = true;
	
	for (int i = 2; i * i < N+1; i++) {
		for (int k = i * i; k < N+1; k += i) {
			b[k] = false;
		}
	}

	// 결과
	cout << N << "까지의 소수들\n";
	for (int i = 2; i < N + 1; i++) if (b[i]) cout << i << ", ";

	cout << "\n\n" << N2 << "는 ";
	if (sosu(N2)) cout << "소수입니다.\n";
	else cout << "소수가 아닙니다.\n";

	return 0;
}

#pragma once
#include <cctype>
#include <cerrno>
#include <cfloat>
#include <ciso646>
#include <climits>
#include <clocale>
#include <cmath>
#include <csetjmp>
#include <csignal>
#include <cstdarg>
#include <cstddef>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>

#include <ccomplex>
#include <cfenv>
#include <cinttypes>
#include <cstdalign>
#include <cstdbool>
#include <cstdint>
#include <ctgmath>
#include <cwchar>
#include <cwctype>

// C++
#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <exception>
#include <fstream>
#include <functional>
#include <iomanip>
#include <ios>
#include <iosfwd>
#include <iostream>
#include <istream>
#include <iterator>
#include <limits>
#include <list>
#include <locale>
#include <map>
#include <memory>
#include <new>
#include <numeric>
#include <ostream>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <stdexcept>
#include <streambuf>
#include <string>
#include <typeinfo>
#include <utility>
#include <valarray>
#include <vector>
#include <array>
#include <atomic>
#include <chrono>
#include <condition_variable>
#include <forward_list>
#include <future>
#include <initializer_list>
#include <mutex>
#include <random>
#include <ratio>
#include <regex>
#include <scoped_allocator>
#include <system_error>
#include <thread>
#include <tuple>
#include <typeindex>
#include <type_traits>
#include <unordered_map>
#include <unordered_set>

#include <iostream>

using namespace std;

int gcd(int a, int b) {
	return b ? gcd(b, a % b) : a;
}

int main() {

	cout << gcd(25, 45) << "\n";
	cout << 15*45/gcd(15, 45) << "\n";

	return 0;
}

#include <string>
#include <vector>
#include <iostream>

using namespace std;

vector<vector<int>> result;
vector<int> v = { 1,2,3,4,5 };
int len = v.size();
vector<int> sub;

void ser(int k) {

    if (k == len  ) {
        result.push_back(sub);
    }
    else {
        sub.push_back(v[k]);
        ser( k + 1);
        sub.pop_back();
        ser( k + 1);
    }
}

int main()
{
    ser(0);

    for (int i = 0; i < result.size(); i++) {
        for (int k = 0; k < result[i].size(); k++) {
            cout << result[i][k];
        }
        cout << "\n";
    }

    return 0;
}