1. Chapter 5 Input and Output Streams

2. 5.1 Input and Output Streams
I/O (Input and Output) incorporates streams or flows of information
Flow runs from input device (keyboard) into program
Flow runs from program to an output device (console window or screen)
Need to include <iostream>

3. 5.1.1 Namespaces and I/O Streams
Three Options for accessing individual components of the header file – Method 3 preferred
// Method 1 -- PREFERRED METHOD
#include <iostream>
using namespace std;
...
cout << "Hello World";
// Method 2
std::cout << "Hello World";
// Method 3
using std::cout;

4. 5.1.2 The cout Statement Displays information to the screen
cout represents console output
Information displayed includes literals, constants and variables
cout << "Hello World"; // Writes the literal “Hello World” to the screen
Insertion operator ( << ) Inserts the information into the cout stream

5. 5.1.2 The cout Statement Example with multiple lines:
char grade = 'B';
float class_avg = 88.5;
// Notice there isn’t a semicolon at the // end of the first line
cout << "Your average is: " << class_avg
<< "\nYour grade is: " << grade;
// Output
Your average is: 88.5
Your grade is: B

6. 5.1.3 The cin Statement
Reads data from input stream and stores that value, if possible, into the variable used in the cin statement
cin - console input
Example: reading from keyboard
int score = 0;
cin >> score;
Extraction operator (>>)
Extracts information from the stream

7. 5.1.3 The cin Statement
Right operand of the extraction operator must be a variable or variables
Method 1: Reading multiple values
int score1 = 0, score2 = 0;
cout << "Enter two scores: ";
cin >> score1
>> score2;

8. 5.1.3 The cin Statement
Another Method: Reading multiple values (better approach)
int score1 = 0, score2 = 0;
cout << "Enter first score: ";
cin >> score1;
cout << "Enter second score: ";
cin >> score2;

9. 5.2 The endl Manipulator Moves cursor to the next line
endl stands for end line
Manipulator - command directly placed into the stream
Information inserted into the stream is sent to the output buffer (area in memory)
Information stays in the buffer until signaled to write entire buffer to the screen (i.e., flushing the buffer)

10. 5.2.1 The endl Manipulator Versus '\n'
Both endl and '\n' move the cursor to the next line; only endl flushes the buffer
Preferred method:
Use '\n' when possible unless you need to flush the output buffer
No more than one endl per cout
Use endl only at the end of a cout
float money = F;
cout << "You have $" << money << endl;
cout << "Your turn to buy!" << endl;
// Output
You have $123.45
Your turn to buy!

11. 5.3 Input and Output Buffers
Buffer - area of memory that holds data
Input buffer - holds data to be read via a cin
Output buffer - holds data generated by a cout statement
Speeds up writing to the screen
Faster to write a lot of information once to the output device rather than having multiple writes with one piece of data

12. 5.4 Formatting the Output Stream
Number of options available for formatting output
Two unique ways for formatting cout:
1. Member functions –accessed via cout
Syntax for using cout member functions:
cout.<function_name> ( <parameters> );
Parameters - data we supply to the function

13. 5.4 Formatting the Output Stream
2. Manipulators - commands placed directly into the output stream
Manipulators and member functions basically
accomplish same job

14. 5.4 Formatting Member Functions & Manipulators
Description
<iostream>
<iomanip>
Required header files
.width
setw
Set the total width for the displayed data
.precision
setprecision
Places to the right of the decimal point
.setf( ios::right )
Right
Right justify
.setf( ios::left )
left
Left justify
.setf( ios::fixed )
fixed
Decimal notation
.setf( ios::scientific )
scientific
Scientific notation
.setf( ios::showpos )
showpos
Show sign of all numbers even if positive
.setf( ios::showpoint )
showpoint
Show trailing zeros
.flush
flush
Flushes the output buffer

15. 5.4.1 The .width Member Function and setw Manipulator
width member function and setw manipulator - specify amount of space a piece of data will occupy on the screen
Default - data printed to screen with no additional padding
Padding - spaces on either side of the data
If data doesn’t fill allotted space, the data is padded with spaces

16. 5.4.1 The .width Member Function and setw Manipulator
Which side of data spaces appear on depends upon justification
If right justified, spaces are on left side of the data
If left justified, spaces appear on right
Default, right justified
If the data is larger than the specified width, it will not be truncated; just does not appear with padding

17. 5.4.1 The .width Member Function and setw Manipulator
Strings - usually left justified
Numbers - right justified / decimals aligned
Sample Justification:
Willy Makit
Marcus Sunkenship
Calvin Cowboy

18. 5.4.1 The .width Member Function and setw Manipulator
float money = F;
cout << "You have $";
cout.width( 20 );
cout << money << endl;
// Output
You have $

19. 5.4.1 The setw Manipulator
There are 14 spaces between the literal and the value in money
Always count the decimal point as a character when calculating total space required for output
#include <iostream> // Needed for cout
#include <iomanip> // Needed for setw
using namespace std;
int main() {
float money = F;
cout << "You have $";
cout << setw( 20 ) << money << endl;
return 0; }
// Output
You have $

20. 5.4.2 The .precision Member & setprecision Manipulator
.precision member function and setprecision manipulator - sets number of digits displayed to the right of the decimal place
Unlike .width and setw, these are not volatile - precision remains set until a different value is given

21. 5.4.3 The .setf member function
.setf member function – performs a variety of formatting tasks by incorporating flags
Flag – value that represents a specific setting or state
setf - stands for set flag

22. 5.4.3 The .setf member function
.setf member function – performs a variety of formatting tasks by incorporating flags (continued)
A flag representing the desired formatting function is passed to .setf
For every flag passed to .setf, there is a corresponding manipulator with the same name as the flag

23. 5.4.3 The .setf Member Function Example
#include <iostream>
#include <iomanip> // Needed for manipulators
using namespace std;
int main() {
float money = F;
cout << "You have $";
cout.setf( ios::fixed ); // Decimal notation
cout << setprecision( 2 ) << money << endl;
return 0; }
// Output
You have $123.45

24. 5.4.3 Corresponding Manipulators
For every flag passed to .setf, there is a corresponding manipulator with the same name as the flag
using namespace std;
...
cout << fixed << setprecision( 2 ) << money << endl;
Any flag set can be unset using member function unsetf

25. 5.4.4 The .flush Member and the Flush Manipulator
.flush member function and the manipulator - both flush the output buffer without creating a new line
// Member function
cout.flush();
// Manipulator
cout << flush;

26. 5.5 Debugging
Debugger - set of tools to analyze a program line by line while running
Debugger can only help find logic and runtime errors
Syntax errors must be resolved before an executable is built

27. 5.5.1 Step Into, Step Over, & Step Out
Step Into tool - executes the current line
Line being executed designated by a yellow arrow in the left margin
If current line is a function call or routine, Step Into attempts to step into the code within that function or routine
Usually undesirable if the function or routine is predefined

28. 5.5.1 Step Into, Step Over, & Step Out
Step Over - executes current line without stepping into the code within that function or routine
Toolbar icons & hot keys
Tool
Icon
Hot Key
Step Into
F11
Step Over
F10
Step Out
Shift+F11
Step Out - returns to
where undesirable code was entered

29. 5.5.2 Run to Cursor
Step tools - often time consuming to use to step over each line until an error is encountered in larger programs
Run to Cursor – known working code can be bypassed by placing cursor on any executable line and selecting Run to Cursor
Program runs normally until that line of code has been reached - execution then stops - can continue by using the “step” tools to resume line by line execution

30. 5.5.2 Run to Cursor
Executed by right clicking in code window and choosing Run to Cursor from displayed popup menu
Ctrl + F10 hot key - starts Run to Cursor process

31. 5.5.3 Breakpoints
Breakpoints - accomplish same basic functionality as Run to Cursor
Can have multiple breakpoints located strategically throughout the code
Start Debugging option runs to the first breakpoint

32. 5.5.3 Breakpoints
Once program started using any of the debugging tools, Resume option jumps to next breakpoint
To place a breakpoint on a line of code - click in the left margin on the desired line
Red circle marks the breakpoints

33. 5.5.3 Breakpoints Additional options for working with breakpoints
Toggle Breakpoints (F9) – sets or removes a breakpoint on current line as designated by the cursor
Delete All Breakpoints (Shift + Ctrl + F9) – permanently removes all breakpoints
Disable/Enable All Breakpoints – temporarily turns all breakpoints on or off

34. 5.5.4 Watches
Watches – used to examine contents, or the state, of variables, constants, and expressions
Windows provided: Autos, Locals, and Watch1 - 4
Autos window - shows variables within a few lines of the current line of execution
Locals window - shows variables within current scope
Scope - area in which a variable can be seen (more later)
Watch (1 - 4) - for programmer to examine variables of their choice

35. 5.5.4 Watches
Hovering over a variable while debugging also displays a popup window containing variable’s name and value
Autos watch window

36. Character Input
Reading in a character char ch; cin >> ch; // Reads in any non-blank char cin.get(ch); // Reads in any char cin.ignore(); // Skips over next char in // the input buffer
See pr3-23.cpp and pr3-24.cpp

37. Stream Manipulators Used to control features of an output field
Some affect just the next value displayed
setw(x): Print in a field at least x spaces wide. Use more spaces if specified field width is not big enough.
See pr3-15.cpp and pr3-16.cpp

38. Stream Manipulators Some affect values until changed again
fixed: Use decimal notation (not E-notation) for floating-point values.
setprecision(x):
When used with fixed, print floating-point value using x digits after the decimal.
Without fixed, print floating-point value using x significant digits.
showpoint: Always print decimal point for floating-point values.
left, right: left-, right justification of value
See pr3-17.cpp, pr3-18.cpp, pr3-19.cpp, and pr3-20.cpp

39. Manipulator Examples
const float e = 2.718; float price = 18.0; Displays cout << setw(8) << e << endl; ^^^2.718 cout << left << setw(8) << e << endl; 2.718^^^ cout << setprecision(2); cout << e << endl; 2.7 cout << fixed << e << endl; 2.72 cout << setw(6) << price; ^18.00
See pr3-15.cpp through pr3-21.cpp

40. 3.9 Working with Characters and String Objects
char: holds a single character string: holds a sequence of characters Both can be used in assignment statements Both can be displayed with cout and <<

41. String Input
Reading in a string object string str; cin >> str; // Reads in a string // with no blanks getline(cin, str); // Reads in a string // that may contain // blanks
See pr3-21.cpp and pr3-22.cpp

42. Character Input
Reading in a character char ch; cin >> ch; // Reads in any non-blank char cin.get(ch); // Reads in any char cin.ignore(); // Skips over next char in // the input buffer
See pr3-23.cpp and pr3-24.cpp

43. String Operators
= Assigns a value to a string string words; words = "Tasty "; + Joins two strings together string s1 = "hot", s2 = "dog"; string food = s1 + s2; // food = "hotdog" += Concatenates a string onto the end of another one words += food; // words now = "Tasty hotdog"