sairate
c34823a3bd
- 新增现代 C++ 教程的 Preface 章节，包括英文和中文版本 - 添加 C++ Primer 练习代码 - 新增 Learn C++ 教程的 C++ 开发简介章节 - 添加头文件解析文档 - 更新 mkdocs.yml，包含新教程的目录结构 - 修改项目设置，使用 Python 3.10环境
477 lines
10 KiB
Markdown
477 lines
10 KiB
Markdown
---
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sort: 1
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---
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# 开始
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## 练习1.1
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查阅你使用的编译器的文档，确定它所使用的文件名约定。编译并运行第2页的main程序。
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解：
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- ``g++ 1.1.cpp -o main``
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- ``./main``
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## 练习1.2
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改写程序，让它返回-1。返回值-1通常被当做程序错误的标识。重新编译并运行你的程序，观察你的系统如何处理main返回的错误标识。
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解：
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- 在ubuntu下，使用g++，返回-1，``./main``没有发现任何异常。
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- ``echo $?``，返回255。
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## 练习1.3
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编写程序，在标准输出上打印Hello, World。
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解：
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```cpp
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#include <iostream>
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int main()
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{
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std::cout << "Hello，World" << std::endl;
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return 0;
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}
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```
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## 练习1.4
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我们的程序使用加法运算符`+`来将两个数相加。编写程序使用乘法运算符`*`，来打印两个数的积。
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解：
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```cpp
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#include <iostream>
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int main() {
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std::cout << "Enter two numbers" << std::endl;
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int v1 = 0, v2 = 0;
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std::cin>> v1 >> v2;
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std::cout << "The product of " << v1 << " and " << v2 << " is "<< v1 * v2 << std::endl;
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}
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```
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## 练习1.5
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我们将所有的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。
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解：
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```cpp
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#include <iostream>
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int main()
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{
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std::cout << "Enter two numbers" << std::endl;
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int v1 = 0, v2 = 0;
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std::cin >> v1 >> v2;
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std::cout << "The product of ";
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std::cout << v1;
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std::cout << " and ";
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std::cout << v2;
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std::cout << " is ";
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std::cout << v1 * v2;
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std::cout << std::endl;
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}
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```
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## 练习1.6
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解释下面程序片段是否合法。
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```cpp
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std::cout << "The sum of " << v1;
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<< " and " << v2;
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<< " is " << v1 + v2 << std::endl;
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```
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如果程序是合法的，它的输出是什么？如果程序不合法，原因何在？应该如何修正？
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解：
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程序不合法，有多余的分号，修改如下：
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```cpp
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std::cout << "The sum of " << v1
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<< " and " << v2
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<< " is " << v1 + v2 << std::endl;
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```
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## 练习1.7
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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。
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解：
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```cpp
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/* 正常注释 /* 嵌套注释 */ 正常注释*/
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```
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错误信息：
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```
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/* 正常注释 /* 嵌套注释 */ 正常注释*/
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^
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ch1.cpp:97:37: error: stray ‘\255’ in program
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ch1.cpp:97:37: error: stray ‘\243’ in program
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ch1.cpp:97:37: error: stray ‘\345’ in program
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ch1.cpp:97:37: error: stray ‘\270’ in program
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ch1.cpp:97:37: error: stray ‘\270’ in program
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ch1.cpp:97:37: error: stray ‘\346’ in program
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ch1.cpp:97:37: error: stray ‘\263’ in program
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ch1.cpp:97:37: error: stray ‘\250’ in program
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ch1.cpp:97:37: error: stray ‘\351’ in program
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ch1.cpp:97:37: error: stray ‘\207’ in program
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ch1.cpp:97:37: error: stray ‘\212’ in program
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ch1.cpp: In function ‘int main()’:
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ch1.cpp:97:50: error: expected primary-expression before ‘/’ token
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/* 正常注释 /* 嵌套注释 */ 正常注释*/
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^
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ch1.cpp:98:5: error: expected primary-expression before ‘return’
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return 0;
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^
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```
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## 练习1.8
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指出下列哪些输出语句是合法的（如果有的话）：
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```cpp
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std::cout << "/*";
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std::cout << "*/";
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std::cout << /* "*/" */;
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std::cout << /* "*/" /* "/*" */;
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```
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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。
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解：
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只有第三句编译出错，改成如下即可：
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```cpp
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std::cout << /* "*/" */";
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```
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第四句等价于输出 `" /* "`。
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## 练习1.9
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编写程序，使用`while`循环将50到100整数相加。
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解：
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```cpp
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#include <iostream>
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int main() {
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int i = 50, sum = 0;
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while (i <= 100) {
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sum += i;
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i += 1;
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}
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std::cout << "sum is " << sum << std::endl;
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}
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```
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## 练习1.10
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除了`++`运算符将运算对象的值增加1之外，还有一个递减运算符`--`实现将值减少1.编写程序与，使用递减运算符在循环中按递减顺序打印出10到0之间的整数。
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解：
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```cpp
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#include <iostream>
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int main() {
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int i = 10;
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while (i >= 0) {
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std::cout << i << std::endl;
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i--;
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}
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}
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```
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## 练习1.11
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编写程序，提示用户输入两个整数，打印出这两个整数所指定的范围内的所有整数。
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解：
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```cpp
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#include <iostream>
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int main() {
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int temp = 0;
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std::cout << "Please enter two numbers"<< std::endl;
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int v1 = 0, v2 = 0;
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std::cin >> v1 >> v2;
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// 若v1 > v2,则调换顺序
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if (v1 > v2) {
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temp = v2;
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v2 = v1;
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v1 = temp;
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}
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while (v1 <= v2){
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std::cout << v1 << std::endl;
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v1 += 1;
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}
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}
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```
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## 练习1.12
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下面的for循环完成了什么功能？sum的终值是多少？
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```cpp
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int sum = 0;
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for (int i = -100; i <= 100; ++i)
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sum += i;
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```
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解：
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从-100加到100，sum的终值是0。
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## 练习1.13
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使用for循环重做1.4.1节中的所有练习（练习1.9到1.11）。
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解：
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### 练习1.9
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```cpp
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#include <iostream>
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// 修改1.9
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int main() {
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int sum = 0;
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for (int i = 50; i <= 100; i++) {
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sum += i;
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}
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std::cout << "sum is " << sum << std::endl;
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}
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```
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### 练习1.10
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```cpp
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#include <iostream>
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int main() {
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for (int i = 10; i >= 0; i--) {
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std::cout << i << std::endl;
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}
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}
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```
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### 练习1.11
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```cpp
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#include <iostream>
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int main() {
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int temp = 0;
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std::cout << "Please enter two numbers"<< std::endl;
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int v1 = 0, v2 = 0;
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std::cin >> v1 >> v2;
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// 若v1 > v2,则调换顺序
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if (v1 > v2) {
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temp = v2;
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v2 = v1;
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v1 = temp;
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}
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for (;v1 <= v2;v1++){
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std::cout << v1 << std::endl;
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}
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}
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```
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## 练习1.14
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对比for循环和while循环，两种形式的优缺点各是什么？
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解：
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- <https://stackoverflow.com/questions/2950931/for-vs-while-in-c-programming>
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-
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```
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The main difference between the `for`'s and the `while`'s is a matter of pragmatics:
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we usually use `for` when there is a known number of iterations,
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and use `while` constructs when the number of iterations in not known in advance.
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The `while` vs `do ... while` issue is also of pragmatics,
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the second executes the instructions once at start,
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and afterwards it behaves just like the simple `while`.
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```
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## 练习1.15
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编写程序，包含第14页“再探编译”中讨论的常见错误。熟悉编译器生成的错误信息。
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解：
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编译器可以检查出的错误有：
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- 语法错误
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- 类型错误
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- 声明错误
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## 练习1.16
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编写程序，从cin读取一组数，输出其和。
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解：
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```cpp
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#include <iostream>
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int main() {
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int sum = 0, value = 0;
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while(std::cin >> value) {
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sum += value;
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}
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std::cout << "sum is " << sum << std::endl;
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return 0;
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}
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```
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## 练习1.17
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如果输入的所有值都是相等的，本节的程序会输出什么？如果没有重复值，输出又会是怎样的？
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## 练习1.18
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编译并运行本节的程序，给它输入全都相等的值。再次运行程序，输入没有重复的值。
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解：
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## 练习1.19
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修改你为1.4.1节练习1.11（第11页）所编写的程序（打印一个范围内的数），使其能处理用户输入的第一个数比第二个数小的情况。
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解：
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```cpp
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#include <iostream>
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int main()
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{
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int start = 0, end = 0;
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std::cout << "Please input two num: ";
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std::cin >> start >> end;
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if (start <= end) {
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while (start <= end){
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std::cout << start << " ";
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++start;
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}
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std::cout << std::endl;
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}
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else{
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std::cout << "start should be smaller than end !!!";
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}
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}
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```
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## 练习1.20
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在网站http://www.informit.com/title/032174113 上，第1章的代码目录包含了头文件 Sales_item.h。将它拷贝到你自己的工作目录中。用它编写一个程序，读取一组书籍销售记录，将每条记录打印到标准输出上。
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解：
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```cpp
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#include <iostream>
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#include "Sales_item.h"
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int main()
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{
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for (Sales_item item; std::cin >> item; std::cout << item << std::endl);
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return 0;
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}
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```
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命令：
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```
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./main < data/add_item
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```
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输出：
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```
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0-201-78345-X 3 60 20
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0-201-78345-X 2 50 25
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```
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## 练习1.21
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编写程序，读取两个 ISBN 相同的 Sales_item 对象，输出他们的和。
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解：
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```cpp
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#include <iostream>
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#include "Sales_item.h"
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int main()
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{
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Sales_item item_1;
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Sales_item item_2;
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std::cin >> item_1;
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std::cout << item_1 << std::endl;
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std::cin >> item_2;
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std::cout << item_2 << std::endl;
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std::cout << "sum of sale items: " << item_1 + item_2 << std::endl;
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return 0;
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}
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```
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命令：
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```
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./main < data/add_item
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```
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输出：
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```
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0-201-78345-X 3 60 20
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0-201-78345-X 2 50 25
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sum of sale items: 0-201-78345-X 5 110 22
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```
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## 练习1.22
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编写程序，读取多个具有相同 ISBN 的销售记录，输出所有记录的和。
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解：
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```cpp
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#include <iostream>
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#include "Sales_item.h"
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int main() {
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Sales_item sum_item;
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for (Sales_item item; std::cin >> item; std::cout << item << std::endl) {
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sum_item += item;
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}
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std::cout << "sum is " << sum_item << std::endl;
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return 0;
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}
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```
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## 练习1.23
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编写程序，读取多条销售记录，并统计每个 ISBN（每本书）有几条销售记录。
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## 练习1.24
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输入表示多个 ISBN 的多条销售记录来测试上一个程序，每个 ISBN 的记录应该聚在一起。
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解：
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```cpp
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#include <iostream>
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#include "Sales_item.h"
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int main()
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{
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Sales_item total;
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if (std::cin >> total){
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Sales_item trans;
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while (std::cin >> trans){
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if (total.isbn() == trans.isbn()) {
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total += trans;
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}
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else {
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std::cout << total << std::endl;
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total = trans;
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}
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}
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std::cout << total << std::endl;
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}
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else {
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std::cerr << "No data?!" << std::endl;
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return -1;
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}
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return 0;
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}
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```
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```
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## 练习1.25
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借助网站上的`Sales_item.h`头文件，编译并运行本节给出的书店程序。
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