1. Chapter 2 part #3 C++ Input / Output
King Saud University
College of Applied studies and Community Service
CSC1101
By: Fatimah Alakeel
Chapter 2 part #3 C++ Input / Output
1st Semester 1436

2. Outline Input / Output Operations Using iostream Output Stream
Input Stream
Common Programming Errors
Fatimah Alakeel
2/17/2012

3. Input/Output Operations
Input operation
an instruction that copies data from an input device into memory.
Input Stream: A stream ( numbers, characters, strings..etc) that flows from an input device ( i.e.: keyboard, disk drive, network connection) to main memory.
Output operation
an instruction that displays information stored in memory to the output devices (such as the monitor)
Output Stream: A stream that flows from main memory to an output device ( i.e.: screen, printer, disk drive, network connection)
Fatimah Alakeel
2/17/2012

4. Using iostream
The C++ iostream library provides hundreds of I/O capabilities.
Standard iostream objects:
cout - object providing a connection to the monitor
cin - object providing a connection to the keyboard
To perform input and output we send messages to one of these objects
Fatimah Alakeel
2/17/2012

5. Output Stream
Fatimah Alakeel
2/17/2012

6. The Insertion Operator (<<)
To send output to the screen we use the insertion operator on the object cout
Format: cout << Expression;
The compiler figures out the type of the object and prints it out appropriately
cout << 5; // Outputs 5
cout << 4.1; // Outputs 4.1
cout << “String”; // Outputs String
cout << ‘\n’; // Outputs a newline
Fatimah Alakeel
2/17/2012

7. Stream-Insertion Operator
<< is overloaded to output built-in types ( ex. int, float,…etc)
Can also be used to output user-defined types (i.e. user defined classes).
cout << ‘\n’;
Prints newline character
cout << endl;
endl is a stream manipulator that issues a newline character and flushes the output buffer
cout << flush;
flush flushes the output buffer
a buffer is just a pre-allocated area of memory where you store your data while you're processing it.
Fatimah Alakeel
2/17/2012

8. Cascading Stream-Insertion Operators
<< : Associates from left to right, and returns a reference to its left-operand object (i.e. cout).
This enables cascading
cout << "How" << " are" << " you?";
Make sure to use parenthesis:
cout << "1 + 2 = " << (1 + 2);
NOT
cout << "1 + 2 = " << 1 + 2;
Fatimah Alakeel
2/17/2012

9. Printing Variables
cout << someVariable;
cout knows the type of data to output
Must not confuse printing text with printing variables:
int x =12;
cout << x; // prints 12
cout << “x”; // prints x
Fatimah Alakeel
2/17/2012

10. Formatting Stream Output
Performs formatted and unformatted output
Display numbers on different width , filling spaces with Varying precision for floating points
Formatted text outputs
Fatimah Alakeel
2/17/2012

11. III. Significant Digits in Float
If the fixed point format is not specified, the precision field specifies the maximum number of digits to be displayed in total counting both those before and those after the decimal point. (may convert from fixed to scientific to print):
float y = ;
cout.precision(2);
cout << y << '\n'; // Outputs 23
cout.precision(3);
cout << y << '\n'; // Outputs 23.1
Fatimah Alakeel
2/17/2012

12. Using showpoint/noshowpoint
showpoint specify that floating-point numbers (even for whole numbers) should be output with a decimal point, even if they’re zeros. Following the decimal point, as many digits as necessary are written to match the precision.
This setting is reset with stream manipulator noshowpoint.
When the showpoint  manipulator is not set, the decimal point is only written for non-whole numbers.
Fatimah Alakeel
2/17/2012

13. Using showpoint/noshowpoint
#include <iostream> using namespace std; int main () { double a, b, pi; a=30.0; b= ; pi= ; cout.precision (5); cout << showpoint << a << '\t' << b << '\t' << pi << endl; cout << noshowpoint << a << '\t' << b << '\t' << pi << endl; return 0; }
Fatimah Alakeel
2/17/2012

14. IV. Formatting Text
To print text you need to include “” around the text
Cout <<“This is a Beautiful Day” ;
You can add escape sequence for further options.
Fatimah Alakeel
2/17/2012

15. Escape Sequence
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2/17/2012

16. Examples cout<<"Please enter the student's grades:”;
cout<<"The class average is “<< average;
The class average is 95.5
Average = 95.5
cout<<“The total area is “<< area<< “and the total cost is “<< cost << “ S.R.”;
The total area is 60.2 and the total cost is 4530 S.R.
area = 60.2
cost = 4530
Cout<<"The student received an ”<< grade << “ grade in the course.";
The student received an A grade in the course.
grade = ‘A’
Fatimah Alakeel
2/17/2012

17. Examples (Con.)
Cout<<”The grade is << grade << gradesymb;
The grade is A+
grade = ‘A’
gradesymb = ‘+’
Cout<<"I am the first line\n”;
Cout<<“\n I am the second line\n";
I am the first line
I am the second line
Fatimah Alakeel
2/17/2012

18. Cascading Stream-Insertion Operators
Allows creating a single output statement that prints 1 or more type of data
e.g. (1)
int age=25;
cout<<“Sarah is “<<age<<“Years Old”;
Output for both
e.g.
int age=25;
cout<<“Sarah is “;
cout<<age;
cout<<“Years Old”;
Compilers start printing from left to right
Compilers start printing from top to down
Sarah is 25 Years Old

19. Input Stream
Fatimah Alakeel
2/17/2012

20. The Extraction Operator (>>)
To get input from the keyboard we use the extraction operator and the object cin
Format: cin >> Variable;
The compiler figures out the type of the variable and reads in the appropriate type
int X;
float Y;
cin >> X; // Reads in an integer
cin >> Y; // Reads in a float
Fatimah Alakeel
2/17/2012

21. Syntax cin >> someVariable;
cin knows what type of data is to be assigned to someVariable (based on the type of someVariable).
Fatimah Alakeel
2/17/2012

22. >> (stream-extraction)
Stream Input
>> (stream-extraction)
Used to perform stream input
Normally ignores whitespaces (spaces, tabs, newlines) in the input stream.
Returns zero (false) when EOF is encountered, otherwise returns reference to the object from which it was invoked (i.e. cin)
This enables cascaded input
cin >> x >> y;
Fatimah Alakeel
2/17/2012

23. Stream Input
cin inputs ints, chars, null-terminated strings, string objects
but terminates when encounters space (ASCII character 32)‏
workaround? use the “get” method [ will see that later]
Fatimah Alakeel
2/17/2012

24. Chaining Calls
Multiple uses of the insertion and extraction operator can be chained together:
cout << E1 << E2 << E3 << … ;
cin >> V1 >> V2 >> V3 >> …;
Equivalent to performing the set of insertion or extraction operators one at a time
Example
cout << “Total sales are $” << sales << ‘\n’;
cin >> Sales1 >> Sales2 >> Sales3;
Fatimah Alakeel
2/17/2012

25. Extraction/Insertion Example
cout << “Hello world! ”;
int i=5;
cout << “The value of i is “ << i << endl;
OUTPUT:
Hello World! The value of i is 5 //endl puts a new line
Char letter;
cout << “Please enter the first letter of your name: “;
cin >> letter;
cout<< “Your name starts with “ << letter;
Please enter the first letter of your name: F
Your name starts with F
Fatimah Alakeel
2/17/2012

26. Common Programming Errors
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2/17/2012

27. Common Programming Errors
Debugging  Process removing errors from a program
Three (3) kinds of errors :
Syntax Error
a violation of the C++ grammar rules, detected during program translation (compilation).
statement cannot be translated and program cannot be executed
Fatimah Alakeel
2/17/2012

28. Common Programming Errors cont…
Run-time errors
An attempt to perform an invalid operation, detected during program execution.
Occurs when the program directs the computer to perform an illegal operation, such as dividing a number by zero.
The computer will stop executing the program, and displays a diagnostic message indicates the line where the error was detected
Fatimah Alakeel
2/17/2012

29. Common Programming Errors cont…
Logic Error/Design Error
An error caused by following an incorrect algorithm
Very difficult to detect - it does not cause run-time error and does not display message errors.
The only sign of logic error – incorrect program output
Can be detected by testing the program thoroughly, comparing its output to calculated results
To prevent – carefully desk checking the algorithm and written program before you actually type it
Fatimah Alakeel
2/17/2012