Assignment due

1
Assignment due

• Write a program the generates a random integer
  expression, presents the two operands and the
  result to the user, and asks the user to tell you
  what the operator is, then tells the user if they
  were correct or incorrect and, if incorrect,
  gives the correct answer. The program should loop
  asking the user if they want another problem to
  solve and stop when they dont. It should also
  keep track of the number of correct and incorrect
  answers and report the score when the user is
  finished.

2
C

• Arrays Part I

3
Compile time allocation

• This is something Java does not offer
• Arrays are always allocated on the heap
• Allocate an array of 20 ints
• int array20
• Indices run from 0 to 19 (as in Java)
• Contents are UNITITIALIZED!!!
• Actually, they are arbitrarily initialized
  (memory locations always have values)

4
Check it out

• Create/build/run the following program in
  VisualStudio
• include "stdafx.h"
• include ltiostreamgt
• int _tmain(int argc, _TCHAR argv)
• int uninitialized5
• for (int i 0 i lt 5 i)
• stdcout ltlt uninitializedi ltlt stdendl
• return 0

5
Initialization

• You can do the usual (Java-like) things
• int initialized5
• for (int i 0 i lt 5 i)
• initializedi 0
• or
• int initialized5 0, 0, 0, 0, 0

6
Initialization

• You can also do this, which is sort of allowed
  in Java but does something quite different
• int initialized_05 0
• or
• int initialized_15 1
• Add these lines to your program and print out the
  contents of each array to see what happens.

7
Number of elements in an array

• There is no .length attribute as in Java because
  arrays are not references
• To get the number of elements in an array you
  must do some operations
• int initialized5
• int bytes sizeof(initialized)
• The sizeof() operator returns the number of bytes
  in the data type
• What will the value of the variable bytes be?
• Try it and see

8
Number of elements in an array

• To get the number of elements you need to divide
  the total number of bytes in the array by the
  number of bytes in each element
• int initialized5
• int length sizeof(initialized)
• / sizeof(initialized0)
• Try it

9
Multi-dimensional arrays

• In Java a 2 dimensional array is a 1 dimensional
  array of 1 dimensional arrays
• Not so in C
• Here its a contiguous block of memory with index
  markers

10
Multi-dimensional arrays

• int twoD32

11
Multi-dimensional array initialization

• int twoD32 0, 1, 2, 3, 4, 5
• int twoD32 0, 1, 2, 3, 4, 5
• int twoD32 0, 1
• int twoD32 0, 1
• int twoD32 0, 1, 2 // errorwhy?

12
Multi-dimensional array lengths

• int twoD32
• int rows sizeof(twoD) / sizeof(twoD0)
• int cols sizeof(twoD0) / sizeof(twoD00)

13
Homework Part I

• Test the random number generator
• Create a 1D array of n ints
• Fill the array with random numbers between 0 and
  100
• Compute and report the average of the array
  contents
• Do this for n 10, 100, 1000, 10000, 100000

14
Homework Part II

• Create a 2D array of m x n ints
• Fill the array with random numbers between 0 and
  100
• Compute and report the average of the array
  contents
• Do this for all combinations of m 1, 10, 100
  and n 1, 10, 100, 1000

15
Homework special instructions

• Do not use any hard coded values or constants
  when calculating loop indices
• Use the techniques discussed for computing the
  number of elements in rows/columns of an array
• Due Thursday, next class meeting Ill look at
  your results in class