Syntax/Hints/Help

• Don't confuse testing for equality with assigning a value

          
      == vs =
  
      == tests for equality
      = assigns (from right to left)
  
  
      including a = in an if is usually a mistake
           if (foo = bar)     mistake        
           if (foo == bar)      okay
  

  
  
  
• The % operator ONLY works with type int
  
  
• constructors do NOT have a return type

      void Fraction::Fraction() {
      ^^^^
      wrong
  
  
      }
  
      it should be
  
      Fraction::Fraction() {
  
  
      }
  

  
  
  
• ***** ALL method and function calls must have a pair of ()
  
  
• Don't redeclare a field from a class in your methods

      class Fraction {
      private:
          int num, den;
  
      public:
          void display();
          Fraction();
      };
  
  
      Fraction::Fraction() {
          int num, den;
          ^^^
          wrong
      }
  
      void Fraction::display() {
          int num, den;
          ^^^
          wrong    
      }
  

  
  
  
• if you are unsure how to use #ifndef, #define, and #endif when creating a .h file look at any of the provided .h files for an example

  #ifndef _classname   // _classname is typically indicative of the class in the .h file
  #define _classname
  
  // the class declaration
  class Fraction {
  
      etc.
      
  };    <-- don't forget the semi-colon here
  
  #endif   <-- don't forget the #endif at the very end
  

  
  
  
• to define a constant:

  const int MAX  = 20;
  

  
  
  
• to open the file before reading

      SafeOpenForReading(infile, "File to run with? ");
  
   to read from the file that was just opened:  
   
      infile >> some_name;
  
   to test if the last read from the file failed
  
      if (infile.fail() == true)
  

  
  
  
• to display to the screen use:

      cout << ....;
  

  
  
  
• to read in a value from the keyboard

      cin >> ...;
  

• syntax of an if/elseif/else

  if (test) {
      stmt;
      stmt;
      ...
  } if (test) {
      stmt;
      stmt;
      ...
  } else {
      stmt;
      stmt;
      ...
  }
  

  
  
  
• syntax of a switch

  switch (test) {
      case i1:
              stmt;
              stmt;
              ...
              break;
      case i2:    
              stmt;
              stmt;
              break;
      .
      .
      .
      case n:
              stmt;
              stmt;
              ...
              break;
      default: 
  }
  

  
  
  
• syntax of loops

  while ( test )  
  {
      stmt;
      stmt;
      ...
  }
  
  while ( test )  
  {
      stmt;
      stmt;
      ...
  }
  for (init; test; update) 
  {
      stmt;
      stmt;
      ...
  }
  

  
  
  
• Sample Function Prototypes

      void    fname1(int &number, int count);
      
      // this function will require a return in it
      double    fname3(char letter, double value);            
  

  
  
  
• Sample function prototype with an ifstream parameter it MUST be a reference parameter

      void    read(ifstream & infile)
  

  
  
  
• Sample declarations and function Calls (these match the prototypes shown above)

      char letter;
      double value;
      int number, count;
      
  // sample function calls
                      
      fname1(number,count);    
  
      double answer ;
      answer = fname3(letter,value);
  
      read(infile);    
  

  
  
  
• Sample Function Implementations

      void fname1(int number, int count) {
          
          stmt;
          stmt;
          ...
       }
  
      double    fname3(char letter, double value)
      {
          
          stmt;
          stmt;
          ...
          return (...);
      }
  
  

• Vectors
  • Declaring a Vector of floats

        Vector <float> scores;
        
        Vector <float> scores(5);        
    

    
    
    
  • Vector methods

        Set_Used()
        e.g.
            scores.Set_Used(a value);
        
            
        Used()
        e.g.
            scores.Used(5);
        
            
        Append(a value)
        e.g. 
            scores.Append(26.5);
            
        
        Fill_With(a value)
        e.g. 
            scores.Fill_With(4.1);
    
    
        [a slot number]
        e.g.
            scores[3]        
    

    
    
    
  
  
  
• Matrices
  • Declaring a Matrix of floats

        Matrix <float> mat;
    

    
    
    
  • Matrix methods

        Set_Used(row size, col size)
        e.g.
            mat.Set_Size(4, 5)
        
            
        Set_Size_From_Used()
        e.g.
            mat.Set_Size_From_Used();
        
                    
        Row_Used()
        e.g.
            mat.Row_Used();
        
            
        Col_Used()
        e.g.
            mat.Col_Used();
                    
            
        [a row number][a col number]
        e.g.
            mat[1][3]