Operating System• Using setw and setprecision functions

• Using setiosflags function• Using cin function

Programming 1DCT 1033

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Objectives

In this chapter, you will:

• Discover how to input data into memory using input statements

• Explore how to read data from the standard input device

• Learn how to debug a program using cout statements

• Learn how to debug a program by understanding error messages

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Objectives (continued)

• Explore how to use the input stream functions get, ignore, and clear

• Become familiar with input failure

• Learn how to perform input and output operations with the string data type

• Learn how to format output using the manipulators fixed, showpoint, setprecision, setw, left, and right

• Become familiar with file input and output

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Input (Read) Statement

• The syntax of an input (read) statement using cin and the stream extraction operator >> is:

• During programming execution, if more than one value is entered in a line, these values must be separated by at least one blank or tab– Or, one value per line can be entered

Input (Read) Statement (continued)

Must be included to use cin

So we can refer to cin without using std::

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Variable Initialization

• C++ does not automatically initialize variables when they are declared

• Ways to initialize a variable– By using the assignment statement

feet = 35;

– By using a read statementcin >> feet;• More versatile

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Creating a C++ Program (Revisited)

• In skeleton form, a C++ program looks like this:

preprocessor directives to include header files

using statement

declare named constants, if necessary

int main()

{

variable declaration

statements

return 0;

}

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Programming Style and Form (Revisited)

• In Chapter 1, you learned about syntax, semantics, errors, and how to format a program properly

• In this section, we extend our capabilities to include prompt lines in a program

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Prompt Lines

• Prompt lines: executable statements that tell the user what to do to interact with the program

cout << "Please enter a number between 1 and 10 and then "

<< " press Enter." << endl;

cin >> num;

• Prompt lines should include sufficient information about what input is acceptable

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Debugging – Sprinkling with couts

• Walk-throughs may fail to reveal bugs

• Inserting temporary strategically located cout statements can aid in the debugging process

int fahrenheit = 32;

int celsius = 5 / 9 * (fahrenheit - 32);

cout << fahrenheit << " degrees "

<< "Fahrenheit is " << celsius

<< " degrees " << "Celsius. " << endl;

cout << "5 / 9 is " << 5 / 9

<< " and fahrenheit - 32 is "

<< fahrenheit - 32 << endl;

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Debugging – Understanding Error Messages

• The C++ compiler will find syntactic errors in your program and will provide messages describing the errors– Provide a good indication of where to look for the

problem(s)– Look carefully in the immediate vicinity of the

reported error

• Finding and reporting errors is like peeling away layers of an onion

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Input Failure

• Things can go wrong during execution

• If input data does not match corresponding variables, program may run into problems

• Trying to read a letter into an int or double variable will result in an input failure

• If an error occurs when reading data:– Input stream enters the fail state

Input Failure (continued)

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Input Failure (continued)

• Sample run 1Line 9: Enter four integers: 34 K 67 28

Line 12: The numbers you entered are:

Line 13: a = 34, b = 20, c = 30, d = 40

• Sample run 2Line 9: Enter four integers: 37 653.89 23 76

Line 12: The numbers you entered are:

Line 13: a = 37, b = 653, c = 30, d = 40

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Formatting Output

• Other than writing efficient programs, generating the desired output is one of a programmer’s highest priorities

• In this section, you will learn about various output functions and manipulators that allow you to format your output in a desired way

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setprecision Manipulator

• Syntax is:

• Outputs decimal numbers with up to n decimal places

• Must include the header file iomanip:#include <iomanip>

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fixed Manipulator

• fixed outputs floating-point numbers in a fixed decimal format

• Disable by using the stream member function unsetf

• The manipulator scientific is used to output floating-point numbers in scientific format

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showpoint Manipulator

• showpoint forces output to show the decimal point and trailing zeros

• Examplecout << fixed << showpoint;

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showpoint Manipulator (continued)

• Sample runLine 10: setprecision(2)

Line 11: x = 15.67

Line 12: y = 235.73

Line 13: z = 9525.99

Line 14: setprecision(3)

Line 15: x = 15.674

Line 16: y = 235.730

Line 17: z = 9525.986

Line 18: setprecision(4)

Line 19: x = 15.6740

Line 20: y = 235.7300

Line 21: z = 9525.9864

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setw

• Outputs the value of an expression in specific columns

cout << setw(5) << x << endl;

• If number of columns exceeds the number of columns required by the expression:– Output of the expression is right-justified– Unused columns to the left are filled with spaces

• Must include the header file iomanip

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setw (continued)

• Sample run12345678901234567890

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345 Hi 19

345 76.38 19

19 345 76.38

34519

345 19

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left and right Manipulators

• left: left-justifies the output

• right: right-justifies the output

left and right Manipulators (continued)

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left and right Manipulators (continued)

• Sample run12345678901234567890

15 7634 Warm

15 7634 Warm

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Summary

• Input from the standard input device is accomplished by using cin and >>

• >> is the stream extraction operator

• When data is input in a program, the data items are usually separated by blanks, lines, or tabs

• When inputting data into a variable, >> skips all leading whitespace characters

• To use cin, include the header file iostream• Prompt lines: executable statements that tell user

what to do

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Summary (continued)

• setprecision, fixed, showpoint, setw, left, and right can be used to format output

• Include iomanip to use setprecision and setw