第一章

1.3

//1.3
#include <iostream>

using namespace std;

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

1.4

//1.4
#include <iostream>

using namespace std;

int main() {

    std::cout << "Enter two numbers:" << std::endl;
    int v1 = 0, v2 = 0;
    std::cin >> v1 >> v2;
    std::cout << "The sum of " << v1 << " and " << v2
              << " is " << v1 + v2 << std::endl;
    std::cout << "The mul of " << v1 << " and " << v2
              << " is " << v1 * v2 << std::endl;
    return 0;
}

1.5

//1.5
#include <iostream>

using namespace std;

int main() {

    std::cout << "Enter two numbers:" << std::endl;
    int v1 = 0, v2 = 0;
    std::cin >> v1 >> v2;
    std::cout << "The sum of ";
    std::cout << v1;
    std::cout << " and ";
    std::cout << v2;
    std::cout << " is ";
    std::cout << v1 + v2;
    std::cout << std::endl;


    std::cout << "The mul of ";
    std::cout << v1;
    std::cout << " and ";
    std::cout << v2;
    std::cout << " is ";
    std::cout << v1 * v2;
    std::cout << std::endl;
    
    return 0;
}

1.6：解释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，它会输出什么？
The sum of v1
❓如果程序不合法，原因何在？
' ; '代表了程序的一条语句的结束，剩下的语句不知道写入哪一个ostream对象当中

  << " and " << v2;
  << " is " << v1 + v2 << std::endl;

❓应该如何修正？

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

1.3节练习

1.7 编译一个包含不正确的嵌套注释的程序，观察编译器返回的错误信息

代码

#include <iostream>
using namespace std;

/*
 * 注释对/* */不能嵌套
 * "不能嵌套"几个字会被认为是源码
 * 像剩余程序一样处理
 */

int main() {
    return 0;
}

错误信息：

main.cpp:7:13: warning: '/*' within block comment [-Wcomment]
 * 注释对/* */不能嵌套
         ^
main.cpp:7:18: error: unknown type name '不能嵌套'
 * 注释对/* */不能嵌套
              ^
main.cpp:8:4: error: expected unqualified-id
 * "不能嵌套"几个字会被认为是源码
   ^
1 warning and 2 errors generated.
make[3]: *** [CMakeFiles/C___Primer.dir/main.cpp.o] Error 1
make[2]: *** [CMakeFiles/C___Primer.dir/all] Error 2
make[1]: *** [CMakeFiles/C___Primer.dir/rule] Error 2
make: *** [C___Primer] Error 2

1.8 指出下列哪些输出语句是合法的（如果有的话）：

    std::cout << "/*";
    std::cout << "*/";
    std::cout << /* "*/" */;
    std::cout << /* "*/" /* "/*" */;

预测编译这些语句会产生什么样的结果，实际编译这些语句来验证你的答案（编写一个小程序，每次将上述一条语句作为其主体），改正每个编译错误

    std::cout << "/*";    输出：/*
    std::cout << "*/";      输出：*/
    std::cout << /* "*/" */;    报错
    std::cout << /* "*/" /* "/*" */; 输出：/*

报错信息 及 代码

错误代码：
   std::cout << /* "*/" */;
报错信息：
main.cpp:8:24: warning: missing terminating '"' character [-Winvalid-pp-token]
    std::cout << /* "*/" */;
                       ^
main.cpp:8:24: error: expected expression
1 warning and 1 error generated.

更正代码

std::cout << /* "*/" */";    输出*/