1.2 初识输入输出

练习 1.3

编写程序，在标准输出上打印Hello, World。

#include <iostream>

int main()
{
    std::cout << "Helllo World" << std::endl;
    return 0;
}

练习 1.4

我们的程序使用假发运算符+来将两个数相加。编写程序使用乘法运算符*，来法印两个数的积。

#include <iostream>

int main()
{
    std::cout << "The Sub of " << 2 << " and " << 2 << " is " << 2 * 2 << std::endl;

    return 0;
}

练习 1.5

我们将所有输出操作放在一条很长的语句中。重写程序，将每个运算对象的打印操作放在一条独立的语句中。

#include <iostream>

int main()
{
    int a = 0, b = 0;
    a = 2, b = 2;
    std::cout << "The Sub of ";
    std::cout << a;
    std::cout << " and "; 
    std::cout << b; 
    std::cout << " is ";
    std::cout << a*b << std::endl;

    return 0;
}

练习 1.6

解析下面程序片段是否合法。

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

如果程序是合法的，它输出什么？如果程序不合法， 原因何在？应该如何修正？

#include <iostream>

int main()
{
    /*
    int a = 2, b = 2;
    std::cout << "The sum of " << a;
          << " and " << b;
          << " is " << a * b << std::endl;
    //error: expected primary-expression before ‘<<’ token
    */

    int a = 2, b = 2;
    std::cout << "The sum of " << a;
    std::cout << " and " << b;
    std::cout << " is " << a * b << std::endl;

    return 0;
}