Arrays in Computing Fundamentals: Definition, Indexing, and Examples, Slides of Computer Fundamentals

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ISE105: Computing Fundamentals

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Chapter 6 - Arrays

Outline 6.1 Introduction 6.2 Arrays 6.3 Declaring Arrays 6.4 Examples Using Arrays

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6.1 Introduction

• Arrays
  • Structures of related data items
  • Static entity – same size throughout program
  • Dynamic data structures discussed later

Data Structures : “In computer science, a data structure is a particular way of storing and organizing data in a computer so that it can be used efficiently” (NIST)

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Arrays

• Problem statement:
  • Store total marks of 90 students in a class
  • Need to find average of class.
  • Assign grades to each student based on his marks
• Usual way:
  • Use 90 variables to store student information 
  • Do manipulation on them (average etc)
  • Use another 90 variables to store grades. 
• Any better idea ??

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6.2 Arrays

• Array
  • Group of consecutive memory locations
  • Same name and type
• To refer to an element, specify
  • Array name
  • Position number
• Format: arrayname [ position number ]
  • First element at position 0
  • n element array named c:
    • c[ 0 ], c[ 1 ]...c[ n – 1 ]

Namethat ofall array elements (Note of this array have the same name, c)

Positionthe element number within of array c

c[6]

• 6 0 72 1543

0 62

1 6453 78

c[0] c[1] c[2] c[3]

c[11]

c[10]

c[9]

c[8]

c[7]

c[5]

c[4]

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6.3 Defining Arrays

• When defining arrays, specify
  • Name
  • Type of array
  • Number of elements arrayType arrayName[ numberOfElements ]; // [] subscript operator
  • Examples: int c[ 10 ]; float myArray[ 3284 ];
• Defining multiple arrays of same type
  • Format similar to regular variables
  • Example: int b[ 100 ], x[ 27 ]; int age [10] , height [10] , names [20] ; int i , j , age [10] ;

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Array indexing

• The index always runs from 0 to (n-1) inclusive, and NOT 1 to n.
• Index should be a positive integer
• First element at index 0
• Last element at index n-
  • Example: int day[7];
• day[0] to day[6] are legal, but day[7] is not.
• day[0] is the first slot
• day[6] is the seventh slot

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Array indexing

int age[10]; Accessing 5 th^ element of the array c=age[3+2]; OR i=2; c=age[i+3];

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Example1: Using Arrays

• Array elements are like normal variables int age[5],i; for ( i = 0 ; i < 5 ; i ++ ) { scanf("%d",&age[i]); }

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Example 2

int totalAge = 0 ; int age[10]; for ( i = 0 ; i < 10 ; i ++ ) { totalAge + = age [ i ] ; }

Outline

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Program Output

Element 0 Value 0 (^12 ) (^34 ) (^56 ) (^78 ) 9 0

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Copying Arrays

• Data types should be identical
  • Size should be same
• int a [ 10 ] ;
• int b [ 10 ] ;

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Example: 4

• Take the sum of squares of 10 different numbers which are stored in an array int a [ 10 ] ; int arraySize =10 ; int sumOfSquares = 0 ; for ( i = 0 ; i < arraySize ; i ++ ) { sumOfSquares = sumOfSquares + a [ i ] * a [ i ] ; }

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Example 5

Search a number z in an array

for ( i =0 ; i < 100 ; i ++ ) { if ( z == a [ i ] ) { found = 1 ; break ; } } if ( found == 1 ) printf( “ We found the integer at position %d” ,i) ; else printf( “ The number was not found” );