Accelerated C++：通过示例进行编程实践——练习解答（第0章）

第0章开始

0-0. 编译并运行hello world程序。

//main.cpp#include <iostream>using std::cout;using std::endl;int main(){cout<<"Hello,world!"<<endl; return 0;}

lyj@qt:~/Desktop$ g++ main.cpp -o main
lyj@qt:~/Desktop$ ./main
Hello,world!
lyj@qt:~/Desktop$ 


0-1. 表达式：3 + 4的作用？

3+4仅仅是一个表达式，结果为7，没有副作用产生。

tips：有些表达式计算时会产生影响程序或系统环境状态的副作用，如0-0的输出语句，cout<<"Hello,world!"<<endl;该表达式的值是cout，但是也同时将“Hello,world！"字符串写到了标准输出流输出。

0-2.编写一个程序，使其在运行时输出：This (") is a quote, and this (\) is a backslash。

#include <iostream>using std::cout;using std::endl;int main(){cout<<"This (\") is a quote,and this (\\) is a backslash"<<endl;return 0;}

lyj@qt:~/Desktop$ g++ 0-2.cpp -o 0-2
lyj@qt:~/Desktop$ ./0-2
This (") is a quote,and this (\) is a backslash

0-3. The string literal "\t" represents a tab character; different C++ implementations display tabs in different ways. Experiment with your implementation to learn how it treats tabs.
制表符”\t“，只是在字符常量和字符串常量中是代表一定的距离（比如8个空格），用于增加程序可读性。

#include <iostream>using namespace std;int main(){cout<<"hello\tworld!"<<endl;return 0;}

0-4. Write a program that, when run, writes the Hello, world! program as its output.

 #include <iostream>using std::cout;using std::endl;int helloworld(){cout<<"Hello,World!"<<endl;return 0;}int main(){return helloworld();}

lyj@qt:~/Desktop$ g++ 0-4.cpp -o 0-4
lyj@qt:~/Desktop$ ./0-4
Hello,World!
lyj@qt:~/Desktop$ 
也可以将helloworld()放在一头文件中，而在该cpp文件中include进来。

0-5. Is this a valid program? Why or why not? 

#include <iostream>int main()std::cout << "Hello, world!" << std::endl;

修改后如下：

#include <iostream>int main(){std::cout << "Hello, world!" << std::endl;return 0;}

0-6. Is this a valid program? Why or why not?

#include <iostream>int main(){{{{{{ std::cout << "Hello, world!" << std::endl; }}}}}}

同上，无返回值。

0-7. What about this one?

#include <iostream>int main() {    /* This is a comment that extends over several lines        because it uses /* and */ as its starting and ending delimiters */    std::cout << "Does this work?" << std::endl;    return 0; }

那个在/*,*/之间的and看到了吗，删除其左右注释符即可。

tips：单行注释符”//“；多行注释符”/* .......*/“，配对使用。

0-8. ...and this one?

#include <iostream>int main(){    // This is a comment that extends over several lines    // by using // at the beginning of each line instead of using /*    // or */ to delimit comments.    std::cout << "Does this work?" << std::endl;    return 0;}

注意到第6行，将or后面的注释符移植comments.尾部。

0-9. What is the shortest valid program?

如0-0题，没有输入和输出，也即没有了文件头<iostream>，从而最短程序为：

void main(){}

lyj@qt:~/Desktop$ g++ 0-9.cpp -o 0-9
lyj@qt:~/Desktop$ ./0-9
lyj@qt:~/Desktop$ 

0-10. Rewrite the Hello, world! program so that a newline occurs everywhere that whitespace is allowed in the program.

#include <iostream>using std::cout;using std::endl;int main(){cout<<"Hello,\n world!"<<endl;return 0;}

lyj@qt:~/Desktop$ g++ 0-9.cpp -o 0-9
lyj@qt:~/Desktop$ ./0-9
Hello,
 world!
lyj@qt:~/Desktop$ 

其实可以这么扩展，输入一串字符然后分割，在5.6节我们学了字符串分割函数split()，会扩展程序的通用性。