Formatted input and output

Formatted input and output

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  FORMATTED INPUT ANDOUTPUT
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  Objectives In this chapter,you will: • Learn what a stream is and examine input and output streams • Explore how to read data from the standard input device • Learn how to use predefined functions in a program • Learn how to write data to the standard output device • Discover how to use manipulators in a program to format output 2
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  I/O Streams andStandard I/O Devices • I/O: sequence of bytes (stream of bytes) from source to destination – Bytes are usually characters, unless program requires other types of information • Stream: sequence of characters from source to destination • Input stream: sequence of characters from an input device to the computer • Output stream: sequence of characters from the computer to an output device 3
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  I/O Streams andStandard I/O Devices (cont.) • Use iostream header file to extract (receive) data from keyboard and send output to the screen – Contains definitions of two data types: • istream - input stream • ostream - output stream – Has two variables: • cin - stands for common input • cout - stands for common output 4
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  I/O Streams andStandard I/O Devices (cont.) • To use cin and cout, the preprocessor directive #include <iostream> must be used • Variable declaration is similar to: – istream cin; – ostream cout; • Input stream variables: type istream • Output stream variables: type ostream 5
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  cin and theExtraction Operator >> • The syntax of an input statement using cin and the extraction operator >> is: • The extraction operator >> is binary – Left-side operand is an input stream variable • Example: cin – Right-side operand is a variable 6
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  cin and theExtraction Operator >> (continued) • No difference between a single cin with multiple variables and multiple cin statements with one variable • When scanning, >> skips all whitespace – Blanks and certain nonprintable characters • >> distinguishes between character 2 and number 2 by the right-side operand of >> – If type char or int (or double), the 2 is treated as a character or as a number 2 7
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  cin and theExtraction Operator >> (continued) 8
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  Output and FormattingOutput • Syntax of cout when used with << • Expression is evaluated • Value is printed • Manipulator is used to format the output – Example: endl 9
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  setprecision Manipulator • Syntax: •Outputs decimal numbers with up to n decimal places • Must include the header file iomanip: – #include <iomanip> 10
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  fixed Manipulator • fixedoutputs floating-point numbers in a fixed decimal format – Example: cout << fixed; – Disable by using the stream member function unsetf • Example: cout.unsetf(ios::fixed); • The manipulator scientific is used to output floating-point numbers in scientific format 11
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  showpoint Manipulator • showpointforces output to show the decimal point and trailing zeros • Examples: – cout << showpoint; – cout << fixed << showpoint; 12
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  setw • Outputs thevalue 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 13
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  setfill Manipulator • Outputstream variables can use setfill to fill unused columns with a character • Example: – cout << setfill('#'); 14
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  left and rightManipulators • left: left-justifies the output • Disable left by using unsetf • right: right-justifies the output 15
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  Summary • Stream: infinitesequence of characters from a source to a destination • Input stream: from a source to a computer • Output stream: from a computer to a destination • cin: common input • cout: common output • To use cin and cout, include iostream header 16
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  Summary (continued) • Themanipulators setprecision, fixed, showpoint, setw, setfill, left, and right can be used for formatting output • Include iomanip for the manipulators setprecision, setw, and setfill Source: C++ Programming: From Problem Analysis to Program Design, Fourth Edition 17