1. CHAPTER 2 PART #3 C++ INPUT / OUTPUT 1 st Semester 1434 -1435 King Saud University College of Applied studies and Community Service CSC1101 By: Fatimah Alakeel 2013 Edit: Ghadah Al hadba

2. Outline  Input / Output Operations  Using iostream  Output Stream  Input Stream  Common Programming Errors

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)

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

5. Output Stream

6. The Insertion Operator (<<)  To send output to the screen we use the insertion operator << on the object cout  Format: cout << something; This something can be: 1. Literal e.g cout<<5; 2. Expression e.g cout<<(5+4); 3. Variable or constant e.g cout<<num;

7. The Insertion Operator (<<): Literal  << is overloaded to output built-in types ( ex. int, float,…etc) as well as user-defined types (i.e. user defined classes).  The compiler figures out the type of the object and prints it out appropriately e.g(1): cout << 5; // Outputs 5 e.g(2): cout << 4.1; // Outputs 4.1 e.g(3): cout << “Hello”; // Outputs Hello e.g(4): cout << ‘\n’; // move the cursor to a newline String literals should be surrounded with double quotation marks “ “ character literals should be surrounded with single quotation marks ‘ ‘ Important: escape sequence characters ( such as : \n, \t)can be either embedded into a string or printed alone as e.g (4)

8. The Insertion Operator (<<): Expression  Printing an expression is similar to printing a values since the compiler will calculate then print the resulted value.  Thus, the expression operands should be previously declared and had a value e.g.(1): cout << (5 + 1); // Outputs 6 e.g.(2): int x = 5, y; y = 3; cout << ((x + y)/ 2); // Outputs 4 Important: With expressions make sure to use parenthesis (), to get the expected result (to be explained in detail Later in lect6)

9. The Insertion Operator (<<): Variables and constants  To print the content of a variable of a constant identifier we simply place the identifier name after the insertion operator  cout knows the type of data to output, will be printed probably e.g.(1): int x = 5; const double RATE = 3.14; cout << x; // Outputs 5 cout << RATE; // Outputs 3.14 Important: Must not confuse printing text with printing variables, i.e. don’t surround the variable name with a “ “: int m =12; cout << m; // Outputs 12 cout << “m”; // Outputs m

10. 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 Sarah is 25 Years Old e.g. int age=25; cout<<“Sarah is “; cout<<age; cout<<“Years Old”; Compilers start printing from top to down Compilers start printing from left to right

11. Cascading Stream-Insertion Operators  Allows creating a single output statement that prints 1 or more type of data e.g. (2) cout << "How" << " are" << " you?"; How are you? Output

12. Formatting Stream Output  Performs formatted and unformatted output I. Output of numbers in decimal, octal and hexadecimal using manipulators. II. Display numbers on different width, filling spaces with characters III. Varying precision for floating points IV. Formatted text outputs

13. I. Manipulators  C++ manipulators  C++ provides various stream manipulators that perform formatting tasks.  Manipulators are functions specifically designed to be used in conjunction with the insertion ( >) operators on stream objects.  must include iomanip to use  several are provided to do useful things  you can also create your own

14. Output Manipulators (no args) Manipulators included like arguments in extraction endl - outputs a new line character, flushes output dec - sets int output to decimal hex - sets int output to hexadecimal oct - sets int output to octal How to use? Just print the manipulator you want to convert to ( i.e. dec, hex, or oct) before the intended integer variable How to use? Just print the manipulator you want to convert to ( i.e. dec, hex, or oct) before the intended integer variable

15. Output Manipulators (no args) e.g. #include using namespace std; int main() { int x = 20; cout << x<<“ in hexadecimal is: “<<hex << x << endl; cout << x<<“ in octal is: ”<< oct << x << endl; cout << x<<“ in decimal is: ”<<dec << x << endl; return 0; } 20 in hexadecimal is: 14 20 in octal is: 24 20 in decimal is: 20 Output

16. II. Setting the Width  You can use the width(int)or setw(int) function to set the minimum width for printing a value.  If the printed value is shorter than the minimum width there will be a padding with a space otherwise it will be printed as it is  This function works ONLY for the next insertion command (more on this later): e.g. (1) int x = 42; cout.width(5); cout << x<<endl; cout << x; e.g. (2) cout << setw (10); cout << 77 << endl; 42 Output 77 Output

17. II. Setting the Fill Character  Use the fill(char) or setfill(char) function to set the fill character.  The character remains as the fill character until set again. e.g. (1) int x = 42; cout.width(5); cout.fill(‘*’); cout << x << ‘\n’; e.g. (2) cout << setfill ('x') << setw (10); cout << 77 << endl; ***42 Output xxxxxxxx77 Output

18. III. Significant Digits in Float  Function precision(int) to set the number of significant digits  With fixed:the number of digits to the right of the decimal point (see e.g. (1))  Without fixed : 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) (see e.g. (2))  A call to this function sets the precision for all subsequent output operations until the next precision.

19. III. Significant Digits in Float e.g. (2) [Without fixed] float y = 23.1415; cout.precision(1); cout << y << '\n'; cout.precision(2); cout << y << '\n'; cout.precision(3); cout << y << '\n'; e.g. (1) [With fixed] float y = 12.32; cout<<fixed; //Specify that the value is in fixed-point notation cout.precision(1); cout << y << '\n'; cout.precision(2); cout << y << '\n'; cout.precision(3); cout << y << '\n'; 12.3 12.32 12.320 Output 2e+01 23 23.1 Output

20. 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.

21. Using showpoint/noshowpoint #include using namespace std; int main () { double a, b, pi; a=30.0; b=10000.0; pi=3.14165; cout << a << '\t' << b << '\t' << pi << endl; cout.precision (5); cout << showpoint << a << '\t' << b << '\t' << pi << endl; cout << noshowpoint << a << '\t' << b << '\t' << pi << endl; return 0; } 3010000 3.14165 30.000 10000.3.1416 3010000 3.14165 Output

22. 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.

23. Escape Sequence

24. Examples cout<<"Please enter the student's grades:”; Please enter the student's grades: cout<<"The class average is “<< average; The class average is 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. Cout<<"The student received an ”<< grade << “ grade in the course."; The student received an A grade in the course. Average = 95.5 area = 60.2 cost = 4530 grade = ‘A’

25. Examples (Con.) Cout<<”The grade is << grade << gradesymb; The grade is A+ 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 grade = ‘A’ gradesymb = ‘+’

26. Input Stream

27. 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 e.g. int X; float Y; cin >> X; // Reads in an integer cin >> Y; // Reads in a float

28. Syntax cin >> someVariable ; cin knows what type of data is to be assigned to someVariable (based on the type of someVariable ).

29. 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;

30. 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]

31. 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;

32. 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;OUTPUT: Please enter the first letter of your name: F Your name starts with F

33. Common Programming Errors

34.  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

35. 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

36. 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