Items we have Discussed

Objectives

1. Provide some notes on the items we have discussed while we wrote the fist program.

Notes

• Constants
  • A constant is a named memory location with a given type who's contents can be set one time when the constant is initialized
  • Constants are normally placed in the Global Declaration area.
  • Constants should be employed any time there are numbers that have a meaning.
  • Proffered syntax: const type identifier {value};
  • Older Syntax: const type identifier = value;
  • Naming Convention: constants should be all upper case, with words separated by the underscore.
  • Example: const int OZ_PER_GALLON{128};
  • After they are declared, constants can not be changed.
• Programming Components:
  • Syntax: the rules for constructing programs.
  • Semantics: the meaning of the programming elements.
  • Style or Coding Conventions: the local conventions or rule to make code consistent and readable.
    • The syntax for a while loop is:

      • while (boolean expression) 
           statement; 

    • The semantics are :
      1. Evaluate the boolean expression
         1. If the expression is false, exit the loop.
      2. Execute the body of the loop
      3. Go to step 1.
    • The suggested style is
      • Include the body in a code block.

      • while (boolean expression) {
           body statements;
        } 

• I/O
  • Any file descriptor, including cout, cin can be tested as a boolean expression.
    • If it is true, the last operation on the descriptor was successful
    • If it is false, the last operation was not successful.

  • ifstream inFile;
    
    inFile.open("filename");
    if (!inFile) {
        cout << "Error, could not open file" ;
    }
    
    inFile >> avar
    while (inFile) {
         ...
         inFile >> avar
    } 

  • Both of these cases are appropriate and correct.
• The stream extraction operator.
  • cin >> identifier
  • >> is called the stream extraction operator.
  • It will
    • Skip whitespace
    • Read as much of the data type indicated by identifier as possible.
    • It will stop
      • When it reaches a white space
        • For example, reading a float 3.14 will stop at the white space after the 4.
      • When it gets "enough" data
        • For example input to a character reads a single non-white space character.
      • When it encounters something that is not of the data type desired.
        • For example, when reading into an integer, 34. will stop at the .
    • If successful
      • The data will be stored in the variable.
      • The stream operator will test as true.
    • If unsuccessful
      • No data will be stored in the variable.
      • The stream operator will test as false.
  • Multiple stream extractions can be accomplished in a single statement

  • int a, b, c;
    char letter;
    
    // the following will read in data in the form 
    // 3,4,5
    cin >> a >> letter >> b >> letter >> c ;
    // the above code is teh same as 
    cin >> a;
    cin >> letter;
    cin >> b;
    cin >> letter;
    cin >> c ; 

• Initializing variables
  • It is good practice (and required by me) that you initialize all variables.
  • Two methods
    • type identifier = value
    • type identifier{value}
    • The second
      • Is called uniform or brace initialization.
      • It provides a consistent syntax for all types of objects.
      • Is the preferred method.