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Chapter 3 Input/Output

Chapter 3 Input/Output. Objectives. Stream Read data from keyboard Predefined function Input stream functions Write data to screen Manipulators String I/O File I/O. I/O Streams (one-way one-lane). …This is 87 <br> 9.3 ABt%…. …5 4 Hello 98.3 $%^&amp; $39.00…. Output stream objects.

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Chapter 3 Input/Output

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  1. Chapter 3 Input/Output

  2. Objectives • Stream • Read data from keyboard • Predefined function • Input stream functions • Write data to screen • Manipulators • String I/O • File I/O

  3. I/O Streams (one-way one-lane) …This is 87 \n 9.3 AB\t%… …5 4 Hello 98.3 $%^& $39.00… Output streamobjects Input streamobjects …5 4 Hello 98.3 $%^& $39.00… …This is 87 \n 9.3 AB\t%…

  4. cin and >> • >> skips all whitespace characters so it does not read blank • Input data must match the data type of variable • Redundant input will remain in the stream and be discarded after the program terminates • Input failure

  5. Example 3-1 int a,b; double z; char ch,ch1,ch2; Statement Input Value Stored in Memory 1 cin>>ch; A ch='A' 2 cin>>ch; AB ch='A', 'B' is held for later input 3 cin>>a; 48 a=48 4 cin>>a; 46.35 a=46, .35 is held for later input 5 cin>>z; 74.35 z=74.35 6 cin>>z; 39 z=39.0 7 cin>>z>>a;65.78 38z=65.78, a=38 8 cin>>a>>b; 4 60 a=4, b=60 9 cin>>a>>ch>>z; 57 A 26.9 a=57, ch='A', z=26.9

  6. 10 cin>>a>>ch>>z; 57 A 26.9 a=57, ch='A', z=26.9 11 cin>>a>>ch>>z; 57 A 26.9 a=57, ch='A', z=26.9 12 cin>>a>>ch>>z; 57A26.9 a=57, ch='A', z=26.9 13 cin>>z>>ch>>a; 36.78B34 z=36.78, ch='B', a=34 14 cin>>z>>ch>>a; 36.78 B34 z=36.78, ch='B', a=34 15 cin>>a>>b>>z; 11 34 a=11, b=34, Computerwaits for the nextnumber

  7. 16 cin>>a>>z; 46 32.4 68 a=46, z=32.4, 68 is held for later input • 17 cin>>ch>>a; 256 ch='2', a=56 • 18 cin>>a>>ch; 256 a=256, computer waits for the input value for ch. • 19 cin>>ch1>>ch2; A B ch1 = 'A', ch2 = 'B’

  8. Using Predefined Functions • A function is a set of codes that can accomplish something • C++ library contains many predefined functions that are organized into various header files • To use a predefined function, you must #include the header file into your program

  9. Using Predefined Functions • To call (activate) a function, you need to specify • Name of the function • Number of parameters taken by the function • Type of each parameter • Need to know what the function does • Sometimes also need to know the return type of a function

  10. cin.get() cin.get(charVariable); • Name: get()an identifier followed by () always refer to a function • # of parameter: one • Type of parameter: char variable • Get the first character in the current stream and assign it to charVariable (the character is removed from the stream)

  11. cin.ignore() cin.ignore(intExp, charExp); • Name: ignore() • # of parameters: two • Type of 1st parameter: int expressionType of 2nd parameter: char expression • Ignore the next intExp characters or ignore the input until it encounters the character specified by charExp, whichever comes first (note charExp is removed from the current stream)

  12. cin.putback() cin.putback(charVar); • Name: putback() • # of parameter: one • Type of parameter: char • Put a character specified by charVar back into the stream

  13. cin.peek() cin.peek(); • Name: peek() • # of parameter: none • Type of parameter: none (void) • Return the next character in the input stream, but does not remove that character from the input stream • Return type: charThe returned value can be assigned to a variable or used in an expression

  14. The Dot Notation in the Function Call • A dot must be used between cin and function names • The dot is member access operator • cin is an istream variable (object)get(), ignore(), putback(), peek() are member functions of istream object • “Human can walk, sing, dance …”walk(), sing(), dance() are member functions of human objectTom.walk(); Tom.sing(); Tom.dance();

  15. Input Failure and cin.clear() • Mismatch between input data and corresponding variable causes input stream enter into input failure • All further input statements using that stream are ignored • Can use cin.clear() to return the input stream to a working state (Need to combine with calling cin.ignore() to clear up the stream)

  16. Formatting Output • #include <iomanip> • cout << manipulator << …;

  17. getline() getline(istreamVar, stringVar); or getline(istreamVar, stringVar, charDelimiter); • Stand-alone function, no dot notation • Can read from either keyboard or file depending on the type of istreamVar • Reads until the end of the line or the delimiter if specified, whichever comes first

  18. File I/O • File: an area in secondary storage used to hold information • Plain text file ifstream: for input from file • fstream ofstream: for output to file • #include <fstream>

  19. File I/O Steps • Declare file stream variables (objects) ifstream input; ofstream output; • Associate file stream variables with the source files input.open(“c:\\temp\\data.txt”); output.open(“c:\\temp\\out.txt”); Escape sequence

  20. File I/O Steps • Use file stream variable with <<, >>, or other predefined functions to read and write data • input >> payRate; • output << totalPay << endl; • Close the files • input.close(); • output.close();

  21. More on Opening Files open(fileName, fileOpeningMode);

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