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：解釋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，它會輸出什么？
The sum of v1
?如果程序不合法，原因何在？
' ; '代表了程序的一條語句的結(jié)束，剩下的語句不知道寫入哪一個(gè)ostream對象當(dāng)中

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

?應(yīng)該如何修正？

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

1.3節(jié)練習(xí)

1.7 編譯一個(gè)包含不正確的嵌套注釋的程序，觀察編譯器返回的錯(cuò)誤信息

代碼

#include <iostream>
using namespace std;

/*
 * 注釋對/* */不能嵌套
 * "不能嵌套"幾個(gè)字會被認(rèn)為是源碼
 * 像剩余程序一樣處理
 */

int main() {
    return 0;
}

錯(cuò)誤信息：

main.cpp:7:13: warning: '/*' within block comment [-Wcomment]
 * 注釋對/* */不能嵌套
         ^
main.cpp:7:18: error: unknown type name '不能嵌套'
 * 注釋對/* */不能嵌套
              ^
main.cpp:8:4: error: expected unqualified-id
 * "不能嵌套"幾個(gè)字會被認(rèn)為是源碼
   ^
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 指出下列哪些輸出語句是合法的（如果有的話）：

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

預(yù)測編譯這些語句會產(chǎn)生什么樣的結(jié)果，實(shí)際編譯這些語句來驗(yàn)證你的答案（編寫一個(gè)小程序，每次將上述一條語句作為其主體），改正每個(gè)編譯錯(cuò)誤

    std::cout << "/*";    輸出：/*
    std::cout << "*/";      輸出：*/
    std::cout << /* "*/" */;    報(bào)錯(cuò)
    std::cout << /* "*/" /* "/*" */; 輸出：/*

報(bào)錯(cuò)信息 及 代碼

錯(cuò)誤代碼：
   std::cout << /* "*/" */;
報(bào)錯(cuò)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.

更正代碼

std::cout << /* "*/" */";    輸出*/