C++ Primer Section 1-2_c++ section-优快云博客

Section 1-2

Contents and Thoughts

Objects for I/O Stream

In the header iostream , four objects for I/O stream are defined.

cin — standard input
cout—standard output
cerr—standard error—warnings and error messages
clog—general information about execution of the program

Operators and Operands for I/O stream

<< and >> operators are almost the same.

The left-hand operands should be an object of ostream and istream, respectively.
The right-hand operand should be a value or object, to be written to the ostream or to be written by the value read from istream
The return value is an object of the type ostream or istream . And that is why these two statements are equivalent.

std::cin >> v1 >> v2;
(std::cin >> v1) >> v2;

and vice versa.

Exercise

Exercise 1-3

Write a program to print Hello, World on the standard output.

Solution

In 1-3.cpp

Exercise 1-4

Our program(../Example Code/AddTwoNumbers.cpp) used the addition operator, + , to add two numbers. Write a program that uses the multiplication operator *, to print the product instead.

Solution

In 1-4.cpp

Exercise 1-5

We wrote the output in one large statement. Rewrite the program to use a separate statement to print each operand.

Solution

In 1-5.cpp

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?

Solution

This program fragment is not legal. The operator<< needs two operands. But the operators in line 2 and 3 do not have the left-hand operants which should be an object in ostream.

How to fix it?

Erase all the semicolons except that one in the last line.