Functions

1
Functions

• Dilshad M. Shahid
• New York University
• _at_1999

2
Today

• Random number generation

3
Random Number Generation

• There is a function called rand which will
  generate random numbers
• rand returns an integer value so you could call
  it in this way i rand() / i is of type
  int /
• rand function generates an integer between 0 and
  RAND_MAX
• RAND_MAX is a symbolic constant defined in
  ltstdlib.hgt header file. rand itself is in
  ltstdlib.hgt which you will have to include in your
  program if you want to use the rand function

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Random Number Generation

• Since rand() produces such large numbers we often
  use the following to scale it down, e.g.
  rand() 6
• This would produce (in this case) numbers between
  0 and 5 (all the possible remainders when any
  number is divided by 6)
• Similarly, rand() 4 would return numbers
  between 0 and 3

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Random Number Generation

• If you run a program containing the rand function
  you will notice the same output each time you run
  it
• How come, if rand is generating random numbers?
• The truth is rand actually generates
  pseudo-random numbers

6
Random Number Generation

• To actually produce a different sequence of
  numbers, it has to be conditioned
• This is called randomizing and we use the
  standard library function srand
• srand takes an unsigned integer argument and
  seeds the rand function

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Random Number Generation

• An unsigned int is stored in at least 2 bytes of
  memory (like a regular int) but can only have a
  positive value between 0 and 65535
• An int can have both positive and negative values
  between -32767 and 32767
• srand is also in ltstdlib.hgt

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Random Number Generation

• Check out the 2 examples with rand and srand on
  the web page.
• Please read the comments in the program examples
  carefully.