March 23

• Review New Class Conditions
• Important Dates
  • March 30, Test 2.
  • April 1, Revisions to 3B due.
  • April 6, Revisions to 3C due.
  • April 13 Homework 4 due.
• Homework 3B
  • Notes on how to run the code.
  • What is the problem with this code?

  • void LoadArray(string ary[], size_t & size, size_t MAX, string fileName, string destName){
    
         ifstream inFile;
         size_t i;
     
         inFile.open(fileName);
    
         if (!inFile) {
            cout << filename << " does not exist." << endl;
         } else {
             i = 0;
             while(inFile) {
                inFile >> ary[i];
                i++;
             }
         }
         return;
    }
    

  • Look at this on line
• Homework 3C
  • Review the comments
  • Global Variables
    • What is a global variable?
    • It is a variable that is not declared within the scope of a function.
    • Why is a global variable bad?
      • It is possible to change the value of a global variable anywhere within the program.
      • This means you don't know where the value of the variable was changed.
    • With local variables, youknow that they were created and set within the function.
    • With paramteters, you know that the functions you call may have changed the values
      • This is why we need to understand pass by value and pass by reference.
      • It is also why we use the keyword const.
    • By limiting where variable values can change, we are easily able to determine where incorrect changes to variables are made
    • IE we can debug our programs.
    • Global variables remove this conotrol
      • A global variable, as I said above, can be changed anywhere.
      • It is nearly impossible to tell where the value was changed without fully tracing the code by hand.
      • This makes debugging excedingly difficult.
    • An example please
      • I will give one
        • But to make it effective I would neeed much more code.
        • You should be able to spot the error easily
      • Take a look at global.C in the hw3 class directory.