## 笔记部分
1.1 编写⼀个简单的 C++程序
练习答案
Exercise 1.1: Review the documentation for your compiler and determine what file naming convention it uses. Compile and run the main program from page 2.
Exercise 1.2: Change the program to return -1. A return value of -1 is often treated as an indicator that the program failed. Recompile and rerun your program to see how your system treats a failure indicator from main.
#include<iostream>
int main(){
return -1;
}
Exercise 1.3: Write a program to print Hello, World on the standard output.
#include<iostream>
int main(){
std::cout<<"Hello,World"<<std::endl;
return 0;
}
Exercise 1.4: Our program used the addition operator, +, to add two numbers. Write a program that uses the multiplication operator, *, to print the product instead.
#include<iostream>
int main(){
std::cout<<"Enter two numbers"<<std::endl;
int v1,v2;
std::cin>>v1>>v2;
std::cout<<"The product of "<<v1<<" and "
<<v2<<" is "<<(v1*v2)<<std::endl;
return 0;
}
Exercise 1.5: We wrote the output in one large statement. Rewrite the program to use a separate statement to print each operand.
#include<iostream>
int main(){
std::cout<<"Enter two numbers"<<std::endl;
int v1,v2;
std::cin>>v1>>v2;
std::cout<<"The product of "<<v1<<" and "
<<v2<<" is "<<(v1*v2)<<std::endl;
return 0;
}
Exercise 1.6: Explain whether the following program fragment is legal.
std::cout << "The sum of " << v1;
<< " and " << v2;
<< " is " << v1 + v2 << std::endl;
If the program is legal, what does it do? If the program is not legal, why not? How would you fix it?
不合法，可删除第一第二行的分号或者在这两行前面加上“std::cout”。
一种修改方式
std::cout << "The sum of " << v1
<< " and " << v2
<< " is " << v1 + v2 << std::endl;
Exercise 1.7: Compile a program that has incorrectly nested comments
#include<iostream>
int main(){
/* /**/ */
return 0;
}
Exercise 1.8: Indicate which, if any, of the following output statements are legal:
std::cout << "/*";
std::cout << "*/";
std::cout << /* "*/" */;
std::cout << /* "*/" /* "/*" */;
After you’ve predicted what will happen, test your answers by compiling a program with each of these statements. Correct any errors you encounter.
第一行和第二行不会报错，分别输出“/*”和“**/”
第三行报错，等价于
std::cout << " */;
可改为
std::cout << /* "*/" */";
第四个不会报错，输出“/*”。
Exercise 1.9: Write a program that uses a while to sum the numbers from 50 to 100.
#include<iostream>
int main(){
int va1=50,sum=0;
while(va1<=100){
sum+=va1;
va1++;
}
std::cout<<"The sum of numbers from 50 to 100 is "<<sum<<std::endl;
return 0;
}
输出结果： The sum of numbers from 50 to 100 is 3825
Exercise 1.10: In addition to the ++ operator that adds 1 to its operand, there is a decrement operator (–) that subtracts 1. Use the decrement operator to write a while that prints the numbers from ten down to zero.
#include<iostream>
int main(){
int va1=10,sum=0;
while(va1>=1){
sum+=va1;
va1--;
}
std::cout<<"the result is "<<sum<<std::endl;
}
Exercise 1.11: Write a program that prompts the user for two integers.Print each number in the range specified by those two integers.
#include<iostream>
int main(){
std::cout<<"Enter two numbers"<<std::endl;
int v1,v2;
std::cin>>v1>>v2;
while(v1<=v2){//默认v1<v2
std::cout<<v1<<" ";
v1++;
}
return 0;
}
Exercise 1.12: What does the following for loop do? What is the final value of sum?
int sum = 0;
for (int i = -100; i <= 100; ++i)
sum += i;
计算-100+(-99)+(-98)+…98+99+100，
结果是0。
Exercise 1.13: Rewrite the exercises from § 1.4.1 (p. 13) using for loops.
#include<iostream>
int main(){
int sum=0;
for(int i=1;i<=10;++i)
sum+=i;
std::cout<<sum<<std::endl;
return 0;
}
Exercise 1.14: Compare and contrast the loops that used a for with those using a while. Are there advantages or disadvantages to using either form?
1、在for循环中，循环控制变量的初始化和修改都放在语句头部分，形式较简洁，且特别适用于循环次数已知的情况。
2、在while循环中，循环控制变量的初始化一般放在while语句之前，循环控制变量的修改一般放在循环体中，形式上不如for语句简洁，但它比较适用于循环次数不易预知的情况（用某一条件控制循环）。
3、两种形式各有优点，但它们在功能上是等价的，可以相互转换。
Exercise 1.15: Write programs that contain the common errors discussed in the box on page 16. Familiarize yourself with the messages the compiler generates
略
Exercise 1.16: Write your own version of a program that prints the sum of a set of integers read from cin.
#include<iostream>
int main(){
int v1,sum=0;
std::cout<<"Enter numbers"<<std::endl;
while(std::cin>>v1){
sum+=v1;
}
std::cout<<"the sum of them is "<<sum<<std::endl;
return 0;
}
Exercise 1.17: What happens in the program presented in this section if the input values are all equal? What if there are no duplicated values?
Exercise 1.18: Compile and run the program from this section giving it only equal values as input. Run it again giving it values in which no number is repeated.
略
Exercise 1.19: Revise the program you wrote for the exercises in § 1.4.1 (p.13) that printed a range of numbers so that it handles input in which the first number is smaller than the second.
#include<iostream>
int main(){
int v1,v2;
std::cout<<"Input two numbers"<<std::endl;
std::cin>>v1>>v2;
if(v1>v2){
int t;
t=v1;
v1=v2;
v2=t;
}
while(v1<=v2){
std::cout<<v1<<" ";
v1++;
}
return 0;
}
Exercise 1.20: http://www.informit.com/title/032174113 contains a copy of Sales_item.h in the Chapter 1 code directory. Copy that file to your working directory. Use it to write a program that reads a set of book sales transactions, writing each transaction to the standard output.
#include<iostream>
#include"Sales_item.h"
int main()
{
Sales_item item;
while (std::cin>>item)
std::cout << item<<std::endl;
return 0;
}
Exercise 1.21: Write a program that reads two Sales_item objects that have the same ISBN and produces their sum.
#include<iostream>
#include"Sales_item.h"
int main()
{
Sales_item item1,item2;
std::cout<<"input two items that have the same isbn"<<std::endl;
std::cin>>item1>>item2;
std::cout<<"the sum is "<<item1+item2<<std::endl;
return 0;
}
Exercise 1.22: Write a program that reads several transactions for the same ISBN. Write the sum of all the transactions that were read.
#include<iostream>
#include"Sales_item.h"
int main()
{
Sales_item item,sitem;
std::cin>>sitem;
while(std::cin>>item){
sitem+=item;
}
std::cout<<sitem<<std::endl;
}
Exercise 1.23: Write a program that reads several transactions and counts how many transactions occur for each ISBN.
#include<iostream>
#include"Sales_item.h"
int main()
{
Sales_item curItem,item;
if (std::cin >> curItem) {
int cnt = 1;
while (std::cin >> item) {
if (item == curItem)
++cnt;
else {
std::cout << curItem << " occurs " << cnt << " times" << std::endl;
curItem = item;
cnt = 1;
}
}
std::cout << curItem << " occurs " << cnt << " times" << std::endl;
}
else{
std::cout<<"these's no input of sales item"<<std::endl;
}
return 0;
}
Exercise 1.24: Test the previous program by giving multiple transactions representing multiple ISBNs. The records for each ISBN should be grouped together.
略
Exercise 1.25: Using the Sales_item.h header from the Web site, compile and execute the bookstore program presented in this section.
Sales_item 下载地址：http://www.informit.com/title/032174113
（第一章的代码里）