Chapter 1 Getting Started
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.
Linux/MacOS: cc
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.
# get 8 bits errno of last process
Linux/MacOS: echo $?
Exercise 1.3: Write a program to print Hello, World on the standard output.
#include <iostream>
int main() {
std::cout << "Hello world" << std::endl;
}
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() {
// prompt user to enter two numbers
std::cout << "Enter two numbers:" << std::endl;
int v1 = 0, v2 = 0;
std::cin >> v1 >> v2;
std::cout << "The mul 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.
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;
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, line2, line3 中的 << 运算符缺少ostream对象
std::cout << "The sum of " << v1
<< " and " << v2
<< " is " << v1 + v2 << std::endl;
Exercise 1.7: Compile a program that has incorrectly nested comments.
error: expected primary-expression before '/' token * /
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.
Line 1: legal
Line 2: legal
Line 3: illegal, trick
Line 4: legal
Exercise 1.9: Write a program that uses a while to sum the numbers from 50 to 100.
#include <iostream>
int main() {
int num = 50, sum = 0;
while (num <= 100) {
sum += num++;
}
std::cout << sum << std::endl;
return 0;
}
Exercise 1.10: In addition to the ++ operator that adds 1 to its operand, there is adecrement operator (--) that subtracts 1. Use the decrement operator to write a while that prints the numbers from ten down to zero.
void down() {
int i = 10;
while (i >= 0) {
std::cout << i-- << 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() {
// prompt user to enter two numbers
std::cout << "Enter two numbers:" << std::endl;
int v1 = 0, v2 = 0;
std::cin >> v1 >> v2;
while (v1 < v2) {
std::cout << v1++ << std::endl;
}
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;
Answer: sum(-100,100) => 0
Exercise 1.13: Rewrite the first two exercises from § 1.4.1 (p. 13) using for loops.
#include <iostream>
int main() {
int sum = 0;
for (int i = 50; i <= 100; i++) {
sum += i;
}
std::cout << sum << std::endl;
}
for (int i = 10; i >= 0; i--) {
std::cout << i << std::endl;
}
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?
for: 将循环控制变量的更改聚在一起，方便管理，代码简洁
while: 相比for适用更广，可以表达不便使用for表达的循环
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.
Exercise 1.16: Write your own version of a program that prints the sum of a set of integers read from cin.
int main() {
int num = 50, sum = 0;
while (std::cin >> num) {
sum += num;
}
std::cout << 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?
works well
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.
works well
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.
if (v1 > v2) {
// method 1
//std::swap(v1, v2);
// method 2
v1 = v1 + v2;
v2 = v1 - v2;
v1 = v1 - v2;
}
Exercise 1.20: http://www.informit.com/title/0321714113 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::cin >> item1 >> item2; //read a pair of transactions
if (item1.isbn() == item2.isbn()) {
std::cout << item1 + item2 << std::endl; //print their sum
}
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, sum;
if (std::cin >> sum) {
while (std::cin >> item) {
if (sum.isbn() == item.isbn()) {
sum += item;
}
}
std::cout << sum << std::endl;
}
return 0;
}
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() {
// currVal is the number we're counting; we'll read new values into val
Sales_item currVal, val;
// read first number and ensure that we have data to process
if (std::cin >> currVal) {
int cnt = 1; // store the count for the current value we're processing
while (std::cin >> val) { // read the remaining numbers
if (val.isbn() == currVal.isbn()) // if the values are the same
++cnt; // add 1 to cnt
else { // otherwise, print the count for the previous value
std::cout << currVal.isbn() << " occurs "
<< cnt << " times" << std::endl;
currVal = val; // remember the new value
cnt = 1; // reset the counter
}
}// while loop ends here
// remember to print the count for the last value in the file
std::cout << currVal.isbn() << " occurs "
<< cnt << " times" << std::endl;
}// outermost if statement ends here
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.
1.6小节中的示例程序的思路就是题目1.23的答案
Exercise 1.25: Using the Sales_item.h header from the Web site, compile and execute the bookstore program presented in this section.