c++ primer学习笔记(1)

 

学习笔记只为帮助自己记忆,写的并不严谨,以自己理解为主.若看到此文的人,发现错误请指出,非常感谢.

 

1.简单的c++程序

 

还是以main函数为入口点,可以有返回值,也可以返回值为void,文件后缀名为cpp(以不同编译为准)

int main()
{
    return 0;
}

 

2.标准库

 

即c++的扩展函数库

3.iostream库

 

标准库中用于基本标准输出和输入的库

先看以下两个方法
(1)cin 标准输入 (2)cout 标准输出(c读作see, see-in,see-out)

4.使用iostream库

#include <iostream>

/* Simple main function: Read two numbers and write their sum */
int main()
{
    std::cout << "Enter two numbers:" << std::endl; 

    int v1, v2;
    std::cin >> v1 >> v2;   

    std::cout << "The sum of " << v1 << " and " << v2
              << " is " << v1 + v2 << std::endl;

    return 0;
}

分析上面程序

(1)头文件(header):iostream被称之为
(2)#include:程序要使用标准库,则必须先使用引用该文件,库前后加尖括号
(3)命名空间(namespace):方法被定义在命名空间中,为了防止命名冲突,如命名空间std,副作用则是调用函数的时候要引用命名空间.
(4)作用域操作符(scope operator ::),如std::cout 即使用iostream的cout则需要 namespace +”::"+cout
(5)输出操作符和输入操作符(<<,>>) 如上程序
std::cout << "Enter two numbers:" << std::endl;
先输出"Enter two numbers:" ,iostream的endl表示换行

int v1, v2; std::cin >> v1 >> v2; //用户输入两个数字

接着再输出结果,以下为程序输出结果.

 

5.c++的部分控制结构

 

(1)while语句

 

#include <iostream>

int main()
{
    int sum = 0, val = 1;
    // keep executing the while until val is greater than 10
    while (val <= 10) {
        sum += val;  // assigns sum + val to sum
        ++val;       // add 1 to val
    }
    std::cout << "Sum of 1 to 10 inclusive is " 
              << sum << std::endl;

    return 0;
}

 

输出结果:

(2)for语句

输出结果同上

#include <iostream>
int main()
{
    int sum = 0;

    // sum values from 1 up to 10 inclusive
    for (int val = 1; val <= 10; ++val) 
        sum += val;  // equivalent to sum = sum + val
    
    std::cout << "Sum of 1 to 10 inclusive is " 
              << sum << std::endl;

    return 0;
}

(3)if语句

#include <iostream>
int main()
{
    std::cout << "Enter two numbers:" << std::endl;
    int v1, v2; 
    std::cin >> v1 >> v2; // read input

    // use smaller number as lower bound for summation
    // and larger number as upper bound
    int lower, upper;
    if (v1 <= v2) {
        lower = v1;
        upper = v2;
    } else {
        lower = v2;
        upper = v1;
    }

    int sum = 0;

    // sum values from lower up to and including upper
    for (int val = lower; val <= upper; ++val) 
        sum += val;  // sum = sum + val
    
    std::cout << "Sum of " << lower 
              << " to " << upper 
              << " inclusive is " 
              << sum << std::endl;

    return 0;
}

以上为第一章快速入门,省略类这一部分.