Input

• Basics
  • #include <iostream>
  • cout (the opposite of cin)
  • >> get from, or extraction operator
  • cin >> variable

  • 
    int a;
    float b;
    char c;
    string d;
    
    cin >> a;
    cin >> b;
    cin >> c;
    cin >> d;
    
    cin >> a >> b >> c;
    
        

  • When reading characters
    • cin skips white space
  • When reading strings
    • cin skips white space
    • and reads until the next white space
  • When reading integers
    • cin skips white space
    • possible sign followed by digits.
    • ends at white space, or non digit
  • When reading floats
    • cin skips white space
    • possible sign
    • possible digits
    • possible decimal point
    • possible E
    • possible sign
    • possible digits
    • ends when ...
  • a simple example
    • If you would like you can copy this to your directory on cslab103 by

      cp ~dbennett/130/chapter4/cinexamp.C .
             

  • Write a program that will read the length and width of a box and calculate the area and parameter.

  • The nain problem is that we might try to input to the wrong thing.
    • If we attempt to read a int, but encounter a character the input stream "fails"
    • Unless we do something else, it remains in a state of failure
    • We won't worry about this too much, you may assume your programs have correct input for this class.
    • But you will encounter this when debugging
    • You should allways echo out any input you have read.
    • ie, input followed by output.
  • trace the following

    
    int a;
    float b;
    char c;
    string d;
    
    cin >> a >> b >> c >> d >> a >> a >> c;
    
    // use the same input twice to read this one too
    cin >> d >> a >> c >> a >> c >> b  >> d >> d >> b;
    
    Input Stream:
        12  123.45E6  a word 1 23.45
        

• Dealing with White Space
  • new lines
    • The newline character is '\n'
    • endl produces this
    • so does joe, vi, emacs ... when we press the enter key
    • cin.get(ch) reads the next character from the input stream white space or not.
    • This will be much more useful after we encounter loops.
  • ignore
    • cin.ignore(count, c)
    • Ignores up to count characters or the character c
    • cin.ignore(20,'\n');
    • will ignore 20 characters or until we see a newline (including the new line)
    • Again, more useful when whe get loops.
  • getline(stream,string)
    • Reads from here to the next new line, including spaces
    • Stores this into the string.
    • getline(cin, str);
• Interactive I/O
  • Nothing is worse than a blinking cursor
  • Unless it is a meaningless number
  • Label (with cout statements) all input and output
  • Label (with cout statements) ALL input and output

• Write a program that asks for a person's first last and middle names.

  This program should:

  • print their initials
  • and tell them how long their name is.