1 Lecture 6: Input/Output (II) Introduction to Computer Science Spring 2006

2 Contents 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

3 Writing to Standard Output Syntax of cout when used with << cout<<expression or manipulator <<expression or manipulator...; Expression is evaluated Value is printed Manipulator is used to format the output

4 Formatting Output 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

5 The setw Manipulator setw outputs the value of an expression in specific columns If the 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

6 The flush Function 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(); ostreamVar is an output stream variable flush can be used as a manipulator cout<<flush;

7 Additional Output Formatting Tools Output stream variables can use setfill to fill unused columns with a character left: left-justifies the output ostreamVar<<left; Disable left by using unsetf right: right-justifies the output ostreamVar << right;

8 Types of Manipulators Two types of manipulators: With parameters Without parameters Parameterized: require iomanip header setprecision, setw, and setfill Nonparameterized: require iostream header endl, fixed, showpoint, left, and flush

9 I/O and the string Type An input stream variable (cin) and extraction operator >> can read a string into a variable of the data type string Extraction operator Skips any leading whitespace characters and reading stops at a whitespace character Should not be used to read strings with blanks The function getline Reads until end of the current line Should be used to read strings with blanks

10 File Input/Output File: area in secondary storage to hold info File I/O 1. Include fstream header 2. Declare file stream variables 3. Associate the file stream variables with the input/output sources 4. Use the file stream variables with >>, <<, or other input/output functions 5. Close the filesFile Input/Output

11 End of lecture 6 Thank you!