cpp-入门

1. 变量的定义

变量必须先定义，才可以使用。不能重名。变量定义的方式：

cpp

#include <iostream>

using namespace std;

int main()
{
    int a = 5;
    int b, c = a, d = 10 / 2;

    return 0;
}

常用变量类型及范围：

2. 输入输出

整数的输入输出：

cpp

#include <iostream>

using namespace std;

int main()
{
    int a, b;
    cin >> a >> b;
    cout << a + b << endl;
    return 0;
}

字符串的输入输出：

cpp

#include <iostream>

using namespace std;

int main()
{
    int a, b;
    cin >> a >> b;
    cout << a + b << endl;
    return 0;
}

输入输出多个不同类型的变量：

cpp

#include <iostream>
#include <string>

using namespace std;

int main()
{
    int a, b;
    string str;

    cin >> a;
    cin >> b >> str;

    cout << str << " !!! " << a + b << endl;

    return 0;
}

3. 表达式

整数的加减乘除四则运算：

cpp

#include <iostream>
#include <string>

using namespace std;

int main()
{
    int a = 6 + 3 * 4 / 2 - 2;

    cout << a << endl;

    int b = a * 10 + 5 / 2;

    cout << b << endl;

    cout << 23 * 56 - 78 / 3 << endl;

    return 0;
}

浮点数（小数）的运算：

cpp

#include <iostream>
#include <string>

using namespace std;

int main()
{
    float x = 1.5, y = 3.2;

    cout << x * y << ' ' << x + y << endl;

    cout << x - y << ' ' << x / y << endl;

    return 0;
}

整型变量的自增、自减：

cpp

#include <iostream>
#include <string>

using namespace std;

int main()
{
    int a = 1;
    int b = a ++ ;

    cout << a << ' ' << b << endl;

    int c = ++ a;

    cout << a << ' ' << c << endl;

    return 0;
}

变量的类型转换：

cpp

#include <iostream>
#include <string>

using namespace std;

int main()
{
    float x = 123.12;

    int y = (int)x;

    cout << x << ' ' << y << endl;

    return 0;
}

4. 顺序语句

(1) 输出第二个整数：

cpp

#include <iostream>
#include <string>

using namespace std;

int main()
{
    int a, b, c;
    cin >> a >> b >> c;
    cout << b << endl;
    return 0;
}

(2) 计算 (a + b) * c的值

cpp

#include <iostream>
#include <string>

using namespace std;

int main()
{
    int a, b, c;

    cin >> a >> b >> c;

    cout << (a + b) * c << endl;

    return 0;
}

(3) 带余除法

cpp

#include <iostream>
#include <string>

using namespace std;

int main()
{
    int a, b;

    cin >> a >> b;

    int c = a / b, d = a % b;

    cout << c << ' ' << d << endl;

    return 0;
}

(4) 求反三位数：

cpp

#include <iostream>
#include <string>

using namespace std;

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

    int a = n % 10;
    n = n / 10;
    int b = n % 10;
    n = n / 10;
    int c = n;

    cout << a << b << c << endl;

    return 0;
}

(5) 交换两个整数

cpp

#include <iostream>
#include <string>

using namespace std;

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

    int t = a;
    a = b;
    b = t;

    cout << a << ' ' << b << endl;

    return 0;
}

(6) 输出菱形

cpp

#include <iostream>
#include <string>

using namespace std;

int main()
{
    char c;

    cin >> c;

    cout << "  " << c << endl;
    cout << " " << c << c << c << endl;
    cout << c << c << c << c << c << endl;
    cout << " " << c << c << c << endl;
    cout << "  " << c << endl;

    return 0;
}