[Ch.05] 홍정모의 따라하며 배우는 C++ < 흐름제어>

CH.05 흐름제어

5.1 제어 흐름 개요(Control flow)

 

5.2 조건문 if

#include <iostream>
using namespace std;

int min(int x, int y)
{
	if (x > y)
		return y;
	else
		return x;

	/* if (x > y)	return y;
	else		return x; */

	// return (x > y) ? y : x;

}

int main()
{
	int x;
	cin >> x;

	if (x > 10)
	{
		cout << x << " is greater than 10" << endl;
		cout << "Test 1" << endl;
	}
	else
		cout << x << " not is greater than 10" << endl;

	// if else문 에서 선언된 변수들은 if else문 안에서만 유효함.
	if (1)
	{
		int x = 5;
	}
	else
		int x = 6;

	cout << x << endl;

	if (x > 10)
		cout << "x is greater than 10" << endl;
	else if (x < 10)
		cout << "x not is greater than 10" << endl;
	else // if (x == 10)
		cout << "x is exactly 10" << endl;

	// else는 가장 가까이 있는 if에 붙는다. 하지만 {}을 안치면 봤을때 헷갈릴 수 있으니 명확하게 {}쳐주는 것이 좋다.
	if (x >= 10)
	{
		if (x <= 20)
			cout << "x is between 10 and 20" << endl;
	}
	else
		cout << "..." << endl;

	if (x >= 10)
	{
		if (x <= 20)
			cout << "x is between 10 and 20" << endl;
		else
			cout << "..." << endl;
	}

	int x1, y1;
	cin >> x1 >> y1;

	if (x1 == y1)
		cout << "same numbers" << endl;
	else
		cout << "Not same" << endl;

	if (x1 > 0 && y1 > 0)
		cout << "both numbers are positive" << endl;
	else if (x1 > 0 || y1 > 0)
		cout << "one of the numbers is positive" << endl;
	else
		cout << "Neither number is positive" << endl;
	
	int x2;
	cin >> x2;
	if (x2 > 10)
		cout << "A" << endl;
	else if (x2 == -1)
		return 0;
	else if (x2 < 0)
		cout << "B" << endl;

	
	//1, 2는 같다. null statement.
	if (x > 10) // 1.
		;
	
	if (x > 10) // 2.
	{

	};

	if (x = 1) // x = 1; if(x) 이런 의미.
		cout << x << endl;

	return 0;
}

5.3 switch-case

#include <iostream>
using namespace std;

enum class Colors
{
	BLACK,
	WHITE,
	RED,
	GREEN,
	BLUE
};

void printColorName(Colors color)
{
	/*if (color == Colors::BLACK)
		cout << "Black" << endl;
	else if (color == Colors::WHITE)
		cout << "White" << endl;
	else if ........ 아 귀찮아.. 이때 사용하는게 switch-case임. */ 


	/*switch (color)
	{
		case Colors::BLACK :
			cout << "Black";
		case Colors::BLUE :
			cout << "BLUE";
			......... 아 귀찮아... color를 cast 해보자
	}*/

	switch (static_cast<int>(color))
	{
	case 0:
		cout << "Black" << endl;
		break;
	case 1:
		cout << "White" << endl;
		break;
	case 2:
		cout << "Red" << endl;
		break;
	case 4:
		cout << "Green" << endl;
		break;
	case 5:
		cout << "Blue" << endl;
		break;
	}
}

int main()
{
	//printColorName(Colors::BLACK);

	int x;
	cin >> x;

	// 의도적으로 break;를 안넣을 수도 있다.
	{
		switch (x)
		{
		case 0:
			cout << "Zero";
			break;
		case 1:
			cout << "One";
			break;
		case 2:
			cout << "Two";
			break;
		}

		cout << endl;
	}

	int x1;
	cin >> x1;
	
	switch (x1)
	{
		int a;
		// int b = 5; 변수 선언은 할 수 있지만 초기화는 안된다. 값을 대입하는 건 case문 안에서 해야됨.
		// case문 안에서도 변수 선언 할 수 있다.

	case 0:
		a = 1;
		cout << a << endl;
		break;
	// case문 안에서 변수 선언을 했을때 밖에서 int a; 밖에서 선언 한것과 같은 기능을 수행하기 때문에
	// 다른 case문 안에서 사용 할 수 있다.
	// 하지만 대입값은 각각의 case문 안에서만 사용이 가능하다.
	case 1:
		int y; 
		y = 5;
		break;

	case 2:
		y = 5; // y값 대입을 안해줬을 경우 case 1 안에 있는 y = 5가 실행이 안되기에 garbage값이 들어간다.
		cout << y << endl;

	// default는 case가 없는 모든 경우에 실행됨.
	default:
		cout << "Undefined input" << x1 << endl;
	}

	return 0;
}

 

5.4 goto

#include <iostream>
#include <cmath> // sqrt()

using namespace std;

int main()
{
	double x;

tryAgain : //label

	cout << "Enter a non-negative number" << endl;
	cin >> x;

	if (x < 0.0)
		goto tryAgain;

	cout << sqrt(x) << endl;

	return 0;
}

 

5.5 반복문 while

#include <iostream>
using namespace std;

int main()
{
	int count1 = 0;
	while (1)
	{
		cout << count1 << endl;
		++count1;

		if (count1 == 10) break;
	} 

	////overflow
	//unsigned int count2 = 10;

	//while (count2 >= 0)
	//{
	//	if (count2 == 0) cout << "zero";
	//	else cout << count2 << " ";

	//	count2--;
	//}

	int count = 1;

	while (count < 100)
	{
		if (count % 5 == 0) cout << "Hello " << count << endl;

		count++;
	}

	int outer_count = 1;

	while (outer_count <= 5)
	{
		int inner_count = 1;
		while (inner_count <= outer_count)
		{
			cout << inner_count++ << " ";
		}

		cout << endl;
		++outer_count;
	}

	return 0;
}

practice

- 마지막 반복문의 결과를 거꾸로 출력되게 만들어 보라. (1,2,3,4,5/ 1,2,3,4/ 1,2,3/ 1,2/ 1)

5.6 반복문 do_while

#include <iostream>
using namespace std;

int main()
{
	int selection;

	do
	{
		cout << "1. add" << endl;
		cout << "2. sub" << endl;
		cout << "3. mult" << endl;
		cout << "4. div" << endl;
		cin >> selection;
	} while (selection <= 0 || selection >= 5);

	cout << "You selected " << selection << endl;

	return 0;
}

 

5.7 반복문 for

#include <iostream>
using namespace std;

int pow(int base, int exponent)
{
	int result = 1;

	for (int count = 0; count < exponent; count++)
		result *= base;

	return result;
}


int main()
{
	for (int count2 = 0; count2 < 10; ++count2)
	{
		cout << count2 << endl;
	}

	// cout << count << endl; 실행 안됨.


	int count = 0;
	for (; count < 10; ++count)
	{
		cout << count << endl;
	}

	cout << count << endl; // 실행 가능.


	// while(true)와 같은 무한 루프 가운데에 true 써도 됨.
	/*for (;; ++count)
	{
		cout << count << endl;
	}*/

	for (int i = 0, j = 0; (i + j) < 10; ++i, j += 2)
	{
		cout << i << " " << j << endl;
	}

	for(int j = 0; j < 9; ++j)
		for (int i = 0; i < 9; ++i)
		{
			cout << i << " " << j << endl;
		}

	/* for (unsigned int i = 9; i >= 0; --i)
	 	 cout << i << endl; */

	return 0;
}

 

5.8 break, continue

#include <iostream>
using namespace std;

void breakOrReturn()
{

	while (true)
	{
		char ch;
		cin >> ch;

		if (ch == 'b')
			break; // while이 끝나니 Hello 출력

		if (ch == 'r')
			return; // 함수가 끝나니 Hello 출력 X
	}

	cout << "Hello" << endl;
}

int main()
{
	//int count = 0;
	//while (true)
	//{
	//	cout << count << endl;
	//	if (count == 10) break;
	//	count++;
	//}

	// breakOrReturn();

	for (int i = 0; i < 10; ++i)
	{
		if (i % 2 == 0) continue;

		cout << i << endl;
	}


	int count1(0);

	do
	{
		if (count1 == 5)
			continue;

		cout << count1 << endl;

		count1++;
	} while (++count1 < 10); // while(count < 10)하면 무한루프 걸림.

	//	int count(0);
	//	bool escape_flag = false;

	//	while (!escape_flag)
	//	{
	//		char ch;
	//		cin >> ch;

	//		cout << ch << " " << count++ << endl;

	//		if (ch == 'x')
	//			escape_flag = true;
	//	}

	int count(0);

	while (1)
	{
		char ch;
		cin >> ch;

		cout << ch << " " << count++ << endl;

		if (ch == 'x')
			break;
	}

	return 0;
}

 

5.9 난수 만들기(random numbers)

#include <iostream>
#include <cstdlib> // std::rand(), std::srand()
#include <ctime> // std::time()
#include <random>

using namespace std;

//    *number twister*
//
//    unsigned int PRNG() // Pseudo Random Number Generator
//    {
//        static unsigned int seed = 5523;
//
//        seed = 8253729 * seed + 2396403;
//
//        return seed % 32768;
//    }
//

int getRandomNumber(int min, int max)
{
    static const double fraction = 1.0 / (RAND_MAX + 1.0);

    return min + static_cast<int>((max - min + 1) * (std::rand() * fraction));
}


int main()
{
    // std::srand(5323); //seed
    std::srand(static_cast<unsigned int>(std::time(0))); //debug가 필요하면 seed 고정시켜야됨.

    for (int count = 1; count <= 100; ++count)
    {
       /* cout << std::rand() << "\t";*/
        cout << getRandomNumber(5, 8) << "\t";
        if (count % 5 == 0) cout << endl;
    }

    std::random_device rd;
    std::mt19937_64 mersenne(rd()); // create a mesenne twister
    std::uniform_int_distribution<> dice(1, 6);

    for (int count = 1; count <= 20; ++count)
        cout << dice(mersenne) << endl;

    return 0;
}

 

5.10 std::cin 더 잘 쓰기( ignore(), clear(), fail() )

#include <iostream>
using namespace std;

int getInt()
{
    while (true)
    {
        cout << "Enter an integer number : ";
        int x;
        cin >> x;

        if (std::cin.fail())
        {
            std::cin.clear();
            std::cin.ignore(32767, '\n');
            cout << "Invaild number, please try again" << endl;
        }
        else
        {
            std::cin.ignore(32767, '\n');
            return x;
        }
    }
}

char getOperator()
{
    while (true)
    {
        cout << "Enter an operator (+, -) : ";
        char op;
        cin >> op;
        std::cin.ignore(32767, '\n');

        if (op == '+' || op == '-')
            return op;
        else
            cout << "Invaild operator, please try again" << endl;
    }
}

void printResult(int x, char op, int y)
{
    if (op == '+') cout << x + y << endl;
    else if (op == '-') cout << x - y << endl;
    else {
        cout << "Invalid operator" << endl;
    }
}

int main()
{
    int x = getInt();
    char op = getOperator();
    int y = getInt();

    printResult(x, op, y);

    return 0;
}