Program Input and the Software Design Process ROBERT REAVES

Input Stream  The process of placing values from an outside data set into variables in a program is called input.  Computer reads data into variables.  This is from the standard input device, the keyboard.  NOTE: We will look at file input later.

Input Stream  Think of the input stream as a doorway through which characters come into your program from an input device.  Include inside of the iostream header file.  #include  cin is the stream that is associated with the standard input device.  cin >> name;  cin uses the extraction operator (>>), sometimes pronounced “get from”.  (>>) takes two operands.  Left hand: stream expression (so, this means cin)  Right hand: is a variable we store the input data in.

Input Stream  We can use the (>>) operator several times in a single input statement.  cin >> length >> width;  SAME AS:  cin >> length;  cin >> width;  The (>>) will skip leading whitespace or newlines, but terminate when reads one upon reading input.  You may confuse the (>>) operator and the (<<) operator. Just remember to use the operator that points in the direction which the data is going!

Reading Marker and the Newline Character  Reading Marker keeps track of the point in the input stream where the computer should continue reading.  This can be thought of kind of like a bookmark on your input. =)  The (>>) operator leaves the reading marker on the character following the last piece of data read.  Where does the newline character come from and what is it?

Get Function  We said that the (>>) operator skips whitespace, but what happens if we want an input to be some kind of whitespace?  With the (>>) operator that isn’t possible.  We can use the get function!  Gets the very next character in the input stream without skipping any whitespace characters.  cin.get(ch);  This is associated with the cin, or istream data type. So you must use the dot notation to make this function call.

Ignore Function  Isn’t used very much, but something you will love when you have to use it!  Ignore function is used to skip, read and discard, characters in the input stream.  cin.ignore(200, ‘\n’);  First argument to.ignore() is an int expression and the second being a char value.  int expression: amount of input characters to skip unless char value is found.  char value: skip int expression characters or until this is found.

Reading String Data  How to input a character string into a string variable. Two options.  We can use our (>>)  Stops when it reads whitespace.  string firstname;  string lastname;  cin >> firstname >> lastname;  This is a widely used for input purposes, but it has a drawback.  Cannot be used to input a string with blanks in it.

Getline Function  Getline function does not skip leading whitespace characters and continues until it teaches the newline character.  Doesn’t use dot notation, requires two arguments.  First being your istream or cin in this case, second being your string variable.  getline(cin, string);  Reads and stores the entire input line, embedded blanks and all.  NOTE: newline character is consumed, but not stored into your string.

File Input and Output  Ifstream and ofstream are included inside the fstream header file.  #include  We have learned how to use each one of these with cout and cin. We can now define our own input and output file streams using the ifstream and ofstream type!