Transcript Lecture 1: Overview - City University of New York

Lecture 6: Input/Output (II)
Introduction to Computer Science
Spring 2006
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Contents
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Write data to the standard output device
Use manipulators in a program to format
output
Perform input and output operations with the
string data type
File input and output
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Writing to Standard Output
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Syntax of cout when used with <<
cout<<expression or manipulator
<<expression or manipulator...;
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Expression is evaluated
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Value is printed
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Manipulator is used to format the output
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Formatting Output
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endl manipulator moves output to the
beginning of the next line
setprecision(n) outputs decimal numbers with
up to n decimal places
fixed outputs floating-point numbers in a
fixed decimal format
showpoint forces output to show the decimal
point and trailing zeros
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The setw Manipulator
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setw outputs the value of an expression in
specific columns
If the number of columns exceeds the
number of columns required by the
expression
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Output of the expression is right-justified
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Unused columns to the left are filled with spaces
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The flush Function
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flush clears the buffer, even if it is not full
Unlike endl, it does not move the cursor to
the beginning of the next line
The syntax for flush:
ostreamVar.flush();
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ostreamVar is an output stream variable
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flush can be used as a manipulator
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cout<<flush;
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Additional Output Formatting Tools
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Output stream variables can use setfill to fill
unused columns with a character
left: left-justifies the output
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ostreamVar<<left;
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Disable left by using unsetf
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right: right-justifies the output
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ostreamVar << right;
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Types of Manipulators
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Two types of manipulators:
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With parameters
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Without parameters
Parameterized: require iomanip header
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setprecision, setw, and setfill
Nonparameterized: require iostream header
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endl, fixed, showpoint, left, and flush
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I/O and the string Type
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An input stream variable (cin) and extraction
operator >> can read a string into a variable
of the data type string
Extraction operator
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Skips any leading whitespace characters and
reading stops at a whitespace character
Should not be used to read strings with blanks
The function getline
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Reads until end of the current line
Should be used to read strings with blanks
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File Input/Output
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File: area in secondary storage to hold info
File I/O
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Include fstream header
Declare file stream variables
Associate the file stream variables with the
input/output sources
Use the file stream variables with >>, <<, or
other input/output functions
Close the filesFile Input/Output
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End of lecture 6
Thank you!
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