C Programming Language: Practice 10

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C Programming Language Practice 10

• December 19, 2004

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Overview

• Random Numbers Generator
• rand()
• srand()
• dice
• Array initialization and class exercise

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Rand()
int rand() - returns a pseudo-random integer
between 0 and RAND_MAX (32767).

• include ltstdio.hgt
• include ltstdlib.hgtint main()    int
  i    for (i 0 i lt 5 i)
           printf("d\n",rand())        return
  0

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Seed Definition

• Observation The results of several runs are
  identical.
• Explanation The initial seed used by rand() is
  identical each time.
• The Seed
• Used for the generation of the random numbers.
• Explicitly specified using the srand function.

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srand()

• void srand (unsigned int seed)
• Sets seed as the seed for a new sequence of
  pseudo-random integers to be returned by rand().
• The sequences can be repeatable by calling
  srand() with the same seed value.
• The system time is a good choice as an argument
  for srand. It will be different each time the
  program is run. Thus, results will also be
  different.

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Rand() and Srand()

• unsigned long int next 1
• int rand(void)
• next next1103515245 12345
• return (unsigned int) (next/65536) 32768
• void srand (unsigned int seed)
• next seed

Sets the seed for the rand() function
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srand()

• include ltstdio.hgt
• include ltstdlib.hgt
• include lttime.hgtint main()     int i
• / Set the seed /    srand( time( NULL )
  )   for (i 0 i lt 5 i)         printf("
  d\n",rand()        return 0

srand(time(NULL)) is the same as int seed seed
time(NULL) srand(seed)
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• include ltstdio.hgt
• include ltstdlib.hgt
• int main ()
• int i
• int d1, d2
• int a13 / uses 2..12 /
• for (i 2 i lt 12 i) /
  initialize /
• ai 0
• for (i 0 i lt 1000 i) / Compute /
• d1 rand() 6 1
• d2 rand() 6 1
• ad1 d2 ad1 d2 1 / Count the
  occurrences /
• for (i 2 i lt 12 i) / Print /
• printf ("2d 3d\n", i, ai)
• return 0

ai counts how many times a pair of dice rolled
i.
rand() 6 produces random numbers in the range 0
to 5, rand() 6 1 produces random numbers in
the range 1 to 6.
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Output of dice with rand() and srand()
dice (with rand)
sdice(with srand)
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• int main()
• double numbers 5 3.1, 4.1, 5.9, 2.6,
  5.3
• int arr 100 0
• int a_1 5, 4, 3, 2
• int a_2 4 5, 4, 3, 2
• char str_1 "abcdef"
• char str_2 7 'a', 'b', 'c', 'd', 'e',
  'f', 0
• char str_3 7 97, 98, 99, 100, 101,
  102, 0
• int array2d 3 2 1, 2 ,
• 3, 4 ,
• 5, 6
  
• int array3d 3 2 1 0
• return 0

Identical arrays a_1 and a_2
Identical arrays str_1, str_2 and str_3
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Class Exercise

• Write a program that creates a matrix with the
  multiplication table and then prints it.
• Define a matrix
• int mult_table 10 10
• Fill it with the values of the multiplication
  table.
• Print each entry in the table.

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Required Output
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Basic Conversions

• Conversion from basis B to basis 10 and vice
  versa

• Number of digits
• Digit d of number x in base B