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Arrays & Random number generator

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Arrays & Random number generator. Introduction. Data Types. In addition to arrays and structures, C supports creation and manipulation of the following data structures: Linked lists Stacks Queues Trees. Derived types. Fundamental types. User-defined types. Arrays Functions Pointers. - PowerPoint PPT Presentation

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Page 1: Arrays & Random number generator

+

Arrays & Random number generator

Page 2: Arrays & Random number generator

+Introduction

In addition to arrays and structures, C supports creation and manipulation of the following data structures: Linked lists Stacks Queues Trees

Data Types

Derived types Fundamental types User-defined types

• Arrays• Functions• Pointers

• Integral types• Float types• Character types

• Structures• Unions• Enumerations

Page 3: Arrays & Random number generator

+Introduction

An array is a fixed-size sequenced collection of elements of the same data type. List of temperatures recorded every hour in a day, or a

month, or a year. List of employees in an organization. List of products and their cost sold by a store. Test scores of a class of students. List of customers and their telephone numbers Table of daily rainfall data.

Page 4: Arrays & Random number generator

+Arrays : Declaration

An array declaration tells the compiler how many elements the array contains and what the type is for these elements.

The number enclosed in the brackets indicates the number of elements in the array.

The numbering starts with 0. Candy[0] is the first element.Candy[364] is the 365th and last element.Arrays : Initialization

power[0]

1

power[1]

2

power[2]

4

power[3]

6

power[4]

8

power[5]

16

power[6]

32

power[7]

64

type variable-name [size]

Page 5: Arrays & Random number generator

+Arrays : Initialization

When you use empty brackets to initialize an array, the compiler counts the number of items in the list and makes the array that large.

The sizeof operator gives the size, in bytes, of the object, or type, following it. So sizeof days is the size, in bytes, of the whole array, and sizeof days[0] is the size, in bytes, of one element. Dividing the size of the entire array by the size of one element tells us how many elements are in the array.

Using const with Arrays

The program treat each element in the array as a constant

Page 6: Arrays & Random number generator

+Arrays : Run-time initialization

Array can be explicitly initialized at run time.

The first 50 elements of the array sum are initialized to zeros while the remaining 50 elements are initialized to 1.0 at run time.

We can use scanf() to initialize array

Page 7: Arrays & Random number generator

+Arrays : Run-time initialization: Example

Given the list of marks obtained by a class of 50 students in an annual examination.

43,65,51,27,79,11,56,61,82,09,25,36,07,49,55,63,74,81,49,37,

40,49,16,75,87,91,33,24,58,78,65,56,76,67,45,54,36,63,12,21

73,49,51,19,39,49,68,93,85,59 Write a program to count the number of students belonging to

each of following groups of marks:

0-9, 10-19, 20-29,……,90-100

Page 8: Arrays & Random number generator

+Run-time initialization: Example (cont)

Page 9: Arrays & Random number generator

+Run-time initialization: Example (cont)

Frequency

Groups

Page 10: Arrays & Random number generator

+Arrays : Not initialized

If an array is not initialized, the elements might have any value. The compiler just uses whatever values were already present at those memory locations

Not initialized

Partially initialized

If an array is initialized partially, the remaining elements are set to 0.

Page 11: Arrays & Random number generator

+Assigning Array Values

nonvalid array assignment array assignment

Array Bounds

• It's your responsibility to make sure the program uses indices only in the range 0 through 19, because the compiler won't check for you.

• The compiler is not so forgiving if you have too many list values. This overgenerosity is considered an error.

Page 12: Arrays & Random number generator

+

The compiler doesn't check to see whether the indices are valid. The result of using a bad index is, in the language of the C standard, undefined. That means when you run the program, it might seem to work, it might work oddly, or it might abort.

Again! The compiler doesn't check to see whether the indices are valid.

Page 13: Arrays & Random number generator

+Specifying an Array Size

The array size can be any constant value greater or equal to 1.

Page 14: Arrays & Random number generator

+Operations with array: Example

Write a program to evaluate the following expression

The values of x1,x2,… are read from the terminal

Page 15: Arrays & Random number generator

+Random numbers generator A random number generator (RNG) is a computational or

physical device designed to generate a sequence of numbers or symbols that lack any pattern, i.e. appear random.

In C language library provides two function to generate random numbers: rand() return a pseudo-random integer between 0 and

RAND_MAX (32767) srand(unsigned int seed) sets seed as the seed for a new

sequence of pseudo-random integers to be return by rand();

Page 16: Arrays & Random number generator

+Rand() rand() return a pseudo-random integer between 0 and

RAND_MAX (32767)First run

Second run

Page 17: Arrays & Random number generator

+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

Page 18: Arrays & Random number generator

+srand()

srand(unsigned int seed) sets seed as the seed for a new sequence of pseudo-random integers to be return 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 differnet.

Page 19: Arrays & Random number generator

+rand() and srand()

First run

Second run

Page 20: Arrays & Random number generator

+Example: Dices with rand()

a[i] 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.

First run Second run

Page 21: Arrays & Random number generator

+Example: Dices with srand()

a[i] 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.

First run Second run

Page 22: Arrays & Random number generator

+Problem for self-study

Generate 10 random numbers Print them out Calculate and print out their mean:

Calculate and print out their standard deviation

Page 23: Arrays & Random number generator

+ Solution for the lab problems