Lecture 13 Formatting and Random Numbers

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Lecture 13Formatting andRandom Numbers

• ENGR17 Engineering Programming
• Section 1
• Fall 2001

10/28/01
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Outline

• Formatting output
• Generate random numbers using
• srand
• rand
• time

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Formatting Output

• C Stream Manipulators
• setprecision ( )
• Specify number of decimal places to display in
  the outputs numbers
• Syntax setprecision(number)
• setiosflags( )
• Used to control format of the numeric output
• Syntax setiosflags(formatflag)
• setw( )
• Set width of the output field
• setfill( )
• Set fill character
• Both manipulators are defined in a header file
  named include ltiomanip.hgt
• See programming manuals for details

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Formatting Example

• include ltiostream.hgt
• include ltiomanip.hgt
• void main()
• int number 12
• float real (float) 12.345
• cout ltlt "1234567890\n"
• cout ltlt number ltlt "lt-\n"
• cout ltlt setw(5) ltlt number ltlt "lt-\n"
• cout ltlt setw(5) ltlt setfill('') ltlt number ltlt
  "lt-\n"
• cout ltlt setiosflags(iosshowposiosleft) ltlt
  setw(5) ltlt number ltlt "lt-\n"
• cout ltlt real ltlt "lt-\n"
• cout ltlt setprecision(1) ltlt setiosflags(iosfixed
  ) ltlt real
• ltlt "lt-\n"
• cout ltlt setiosflags(iosscientific) ltlt real ltlt
  "lt-\n"

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Formatting Example
Screen Output
1234567890 12lt- 12lt- 12lt- 12lt- 12.345lt-
12.3lt- 1e001lt- Press any key to continue
There wont be a question on formatting on any of
the tests.
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The displayPrices Function
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Generating Random Numbers

• Ideally, a random number generator can produce a
  sequence of completely unrelated numbers
• Since a computer is by nature deterministic,
  creating truly random numbers is very difficult
  (if not impossible)
• There are built-in C/C functions for creating
  random numbers in a program (rand and srand)
• However, the built-in functions are extremely
  poor at creating truly random numbers
• The numbers the srand and rand create are
  actually related through a fairly simple
  algorithm
• But, for most everyday applications, its ok
• Keep in mind that many other random number
  generators exist that are much better than the
  built-in functions

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rand Function

• Produces the random numbers
• Also referred to as the random number generator
• Generates integers from 0 through RAND_MAX
• Syntax rand()
• Defined in ltstdlib.hgt

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srand Function

• Initializes the random number generator
• Syntax srand(seed)
• time function typically used as the seed
• Syntax for using the time function as the seed
  for the srand function time(NULL)
• srand is defined in ltstdlib.hgt
• time is defined in lttime.hgt

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getRandomNumbers Function

• Write a function that generates two random
  numbers, which should be stored in the firstNum
  and secondNum variables
• Pass in a variable called level that serves the
  following function
• If level1, then generate random numbers between
  1 and 10
• Otherwise, generate random numbers between 10 and
  100
• This type of function would be very useful in a
  game program

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Generating Random Numbers
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Summary

• Formatting output streams
• Generating random numbers

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Example

• Write a function to fill a 1D array with random
  numbers from 0 to 99
• The array itself and the size of the array are
  passed to the function

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Code

• include ltiostream.hgt
• include ltstdlib.hgt
• include lttime.hgt
• void fillArray(int nums, int size)
• void main()
• int nums20
• int size20
• int i
• fillArray(nums, size)
• for(i0 iltsize i)
• cout ltlt numsi ltlt endl
• void fillArray(int nums, int size)
• int i
• srand(time(NULL))
• for (i0 iltsize i)