Arrays

• This is chapter 11.
  • Read up to, but not including 11.4
• Arrays are homogeneous collections of data accessed by index.
  • They are characterized by constant time access to any element.
• Arrays are probably the oldest data structure in programming languages.
  • They, in a very real sense, model memory.
  • We will study c style arrays in this chapter.
    • These are somewhat more difficult to use than other style arrays.
    • But you need a basic understanding of the principles
  • Later in your progress we will learn other style arrays.
• The basic idea is a structure where the elements are accessed by an index, or integer between 0 and the size of the array.
• Any time you have a set of variables like player1, player2, ... you should probably be using an array.
• One word of caution:
  • It is quite easy to allocate a huge amount of memory when using arrays.
  • This will lead to some strange/different syntax.
• To allocate a c style array
  • We need to know the size of the array at compile time.
  • Later we will learn dynamic arrays, but for now.
  • type identifier[const integer expression]
  • type identifier[const integer expression]
• See arrayDemo.cpp.
• Normally with a c style array you must keep track of
  • The capacity or the maximum number of elements an array can hold.
  • The current size or the actual number of elements in the array.
• In the demo, this is good:

  • const size_t MAX_WORDS{10};
    ...
    
    string words[MAX_WORDS];
    size_t wordCount {0};
            

• The index
  • Must be between 0 and the size.
  • But must not be the size.
  • Array positions are an offset from the start of the array.
  • Not a number for the boxes.
• Draw an array and discuss index positions.
  • Memory is contiguous.
  • base + index * size_of (element)
• Index out of bounds errors
  • Look at badArray.cpp
  • Note I have the compiler flags turned off.
  • BUT the compiler can not catch everything.
• Array operations
  • You can :
    • Pass arrays as parameters.
    • But only as pass by pointer, or pass by constant pointer.
    • More on this later.
  • The following don't work, or don't work as expected.
    • Perform direct I/O
    • Perform math
    • Pass by value.
    • Return value of a function
• Note, you can not use scoped enumerations as array index values any longer.