Chapter 3, Problem 1TF

Mark the following statements as true or false.

1. An output stream is a sequence of characters from a computer to an output device. (1)

2. To use cin and cout in a program, the program must include the header file iostream. (1, 2)

3. Suppose pay is a variable of type double. The statement cin >> pay, requires the input of a decimal number. (2)

4. The statement cin >> length; and length >> cin; are equivalent. (2)

5. When the statement cin >> numl >> num2; executes, then after inputting a number into the variable numl the program skips all trailing whitespace characters. (2)

6. To use the predefined function sqrt in a program, the program must include the header file cmath. (3)

7. The statement cin.get (ch); inputs the next nonwhitespace character into the variable ch. (4)

8. When the input stream enters the fail state, the program terminates with an error message. (5)

9. To use the manipulators fixed and showpoint, the program does not require the inclusion of the header file iomanip. (6)

10. The statement cin >> right; sets the input of only the next variable right-justified. (7)

11. To input data from a file, the program must include the header file fstream. (10)

Program Plan Intro

An output stream is a stream from a computer to a destination.

Program Description Answer

An output stream is a sequence of characters from a computer to an output device. Hence, the given statement is “True”.

Explanation of Solution

An output stream is a stream from a computer to a destination, where the destination is an output device such as the computer screen (monitor), file, etc.

Program Plan Intro

To use cin and cout in a program, the program must include the header file iostream. This header file contains the definition of the input and output stream objects, cin and cout.

Program Description Answer

To use cin and cout in a program, the program must include the header file iostream. Hence, the given statement is “True”.

Explanation of Solution

To use cin and cout in a program, the program must include the header file iostream. This header file contains the definition of the input and output stream objects, cin and cout. So we can use these inbuilt objects provided by the standard header files of C++. To use cin and cout, every C++ program must use the preprocessor directive:

#include <iostream>

Program Plan Intro

The extraction operator >> is binary and thus takes two operands. The left-side operand must be an input stream variable, such as cin and the right-hand operand, a variable.

Program Description Answer

Suppose pay is a variable of type double, the statement cin >> pay; does not require the input to be only of a decimal number type. Hence, the given statement is “False”.

Explanation of Solution

The statement cin >> pay; can receive input of both integer and decimal types. If the input is of the integer type, it is converted into a decimal type with zero decimal part and then assigned to the pay variable of double type. If the input is decimal type, then the input is received and assigned to the variable without any conversion.

Program Plan Intro

The extraction operator >> is binary and thus takes two operands. The left-side operand must be an input stream variable, such as cin and the right-hand operand, a variable.

Program Description Answer

The statement cin >> length; and length >> cin; are not equivalent. Hence, the given statement is “False”.

Explanation of Solution

The extraction operator >> is binary and thus takes two operands. The left-side operand must be an input stream variable, such as cin and the right-hand operand, a variable. Since the order of the operands is fixed, the statement length >> cin; is not a valid C++ statement and the order of the operands is incorrect. cin >> length; is a syntactically correct statement.

Program Plan Intro

The extraction operator >> is binary and thus takes two operands. The left-side operand must be an input stream variable, such as cin and the right-hand operand, a variable. A single input statement can read more than one data item by using the operator >> several times. When scanning for the next input, >> skips all whitespace characters. Whitespace characters consist of blanks and non-printable characters, such as tabs and the newline character.

Program Description Answer

When the statement cin >> num1 >> num2; executes, then after inputting a number into the variable num1 the program skips all trailing whitespace characters. Hence, the given statement is “True”.

Explanation of Solution

A single input statement can read more than one data item by using the operator >> several times. When scanning for the next input, >> skips all whitespace characters. Whitespace characters consist of blanks and non-printable characters, such as tabs and the newline character. Hence, after inputting a number in the variable num1, the program skips all trailing whitespace characters and inputs the next number in the variable num2.

Program Plan Intro

C++ comes with a wealth of functions called predefined functions. These predefined functions are organized as a collection of libraries called header files. A particular header file may contain several functions. To use a particular function, one needs to know the name of the function, the return type and parameters to the function. cmath is one such header file which is part of the C++ system and contains functions such as sqrt, pow, etc.

Program Description Answer

To use the predefined function sqrt in a program, the program must include the header file cmath. Hence, the given statement is “True”.

Explanation of Solution

Since sqrt function is included as part of the header file cmath, it should be included using the preprocessor directive as below:

#include <cmath>

Program Plan Intro

The variable cin can access the stream function get, which is used to read character data. The get function inputs the very next character, including whitespace characters, from the input stream and stores it in the memory location passed to it as an argument. The syntax for the command is:

cin.get(varChar);

where carChar is a char type variable.

Program Description Answer

The statement cin.get(ch); can input either the next non-whitespace character or the next whitespace character in the variable ch. Hence, the given statement is “False”.

Explanation of Solution

The statement cin.get(ch); can input either the next non-whitespace character or the next whitespace character in the variable ch. So it is incorrect to say that only the next non-whitespace character is input.

Program Plan Intro

Attempting to read invalid data in a variable causes the input stream to enter the fail state. Once an input failure has occurred, the function clear can be used to restore the input stream to a working state. Once an input stream enters the fail state, all further I/O statements using that stream are ignored and the program continues to execute with whatever values are stored in variables and produces incorrect results.

Program Description Answer

When the input stream enters the fail state, the program does not terminate with an error message. Hence, the given statement is “False”.

Explanation of Solution

When the input stream enters the fail state, the program does not terminate with an error message, instead all further I/O statements using that stream are ignored and the program continues to execute with whatever values are stored in variables and produces incorrect results.

Program Plan Intro

To output floating-point numbers in a fixed decimal format, the manipulator fixed is used. When the computer is instructed to output the decimal number in a fixed decimal format, the output may not show the decimal point and the decimal part. To force the output to show the decimal point and trailing zeros, the manipulator showpoint is used.

Program Description Answer

To use the manipulators fixed and showpoint, the program does not require the inclusion of the header file iomanip. Hence, the given statement is “True”.

Explanation of Solution

To use the manipulators fixed and showpoint, the program does not require the inclusion of the header file iomanip. The iomanip header file is however required to use the manipulators set precision, setfill and setw.

Program Plan Intro

To right-justify the output and the manipulator right, the syntax to set the manipulator right is:

ostreamVar << right;

where ostreamVar is an output variable such as cout.

Program Description Answer

The statement cin >> right; sets the input of all the variables henceforth right-justified. Hence, the given statement is “False”.

Explanation of Solution

The statement cin >> right; sets the input of all the variables henceforth right-justified and not just the next variable. In order to change the setting, it has to be done explicitly using the syntax as follows:

cout.unsetf(ios::right);

Program Plan Intro

For file I/O, the statement #include <fstream> is to be used to include the header file fstream in the program. Also, variables of type ifstream for file input and of type ofstream for file output should be declared. open statements are then used to open input and output files. The header file fstream contains the definitions of ifstream and ofstream.

Program Description Answer

To input data from a file, the program must include the header file fstream. Hence, the given statement is “True”.

Explanation of Solution

To input data from a file, the program must include the header file fstream which contains the definition of ifstream and ofstream types. Variables of these types are then declared and used to open files for input and output.