CppPrimer5_ch01_answers

前言

《CppPrimer5》第一章课后答案

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.

Windows

windows

Linux

Exercise 1.2

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.

Windows

windows

Linux

linux

255? why? please look at this

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 = 0, v2 = 0;
  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 = 0, v2 = 0;
  std::cin >> v1 >> v2;
  std::cout << "The product of ";
  std::cout << v1;
  std::cout << " and ";
  std::cout << v2;
  std::cout << " is ";
  std::cout << v1 * v2;
  std::cout << std::endl;
  return 0;
}

Exercise 1.6

Explain whether the following program fragment is legal.

It’s illegal.

[Error] expected primary-expression before ‘<<’ token

Fixed it: remove the spare semicolons.

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3

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

Exercise 1.7

Compile a program that has incorrectly nested comments.

Example:

/*
* comment pairs /* */ cannot nest.
* ''cannot nest'' is considered source code,
* as is the rest of the program
*/
int main()
{
  return 0;
}

Compiled result(g++):

result

Exercise 1.8

Indicate which, if any, of the following output statements are legal:
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2
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4
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.

Compiled result(g++):

result

Corrected? just added a quote:

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

Output:

/**/ */ /*

Exercise 1.9

Exercise 1.10

Exercise 1.11

Exercise 1.12

What does the following for loop do? What is the final value
of sum?
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int sum = 0;
for (int i = -100; i <= 100; ++i)
sum += i;

the loop sums the numbers from -100 to 100. the final value of sum is zero.

Exercise 1.13

Rewrite the exercises from § 1.4.1 (p. 13) using for loops.

Ex1.9:

#include <iostream>

int main()
{
  int sum = 0;
  for (int i=50; i<=100; ++i)
      sum += i;

  std::cout << "the sum is: " << sum << std::endl;

  return 0;
}

Ex1.10:

#include <iostream>

int main()
{
  for (int i=10; i>=0; --i)
    std::cout << i << std::endl;

  return 0;
}

Ex1.11:

#include <iostream>

int main()
{
  int val_small = 0, val_big = 0;
  std::cout << "please input two integers:";
  std::cin >> val_small >> val_big;

  if (val_small > val_big)
  {
    int tmp = val_small;
    val_small = val_big;
    val_big = tmp;
  }

  for (int i=val_small; i<=val_big; ++i)
    std::cout << i << 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?

If you need a pattern which is using a variable in a condition and incrementing that variable in the
body. You should use for loop. Else the while loop is more simple.

Want to know more? look at this

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.

JUST READ IT!

Exercise 1.16

Write your own version of a program that prints the sum of a set of integers read from cin.

Many people confused about this exercise, such as this and this.

In my opinion, the exercise aim to write the program without “END-OF-FILE“.

BUT, the code in first link is not correct.

The following are my own version:

#include <iostream>

int main()
{
  int limit = 0, sum = 0, value = 0;
  std::cout << "How many integers would you like to enter?";
  std::cin >> limit;

  // assume we don't know what is EOF(End-Of-File).
  while (std::cin >> value && (--limit != 0))
    sum += value;

  std::cout << sum + value << std::endl;

  return 0;
}

Watch out for “sum + value” in the cout line.

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?

If the input values are all equal, it will print a line which shows the count of the number you input.

If there are no duplicated values, when different values input, a new line will be printed if you click Enter.

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.

run

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.

Yes, we should use if to judge which is bigger.

review this code

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.

Here is the code.

You need to enable C++11 support in your compiler.
With GCC and Clang, this can be done with the -std=c++11 option.

(Never say it again.)

How to test it? use the book.txt in data folder. And do it like this:

run