Data Structures - Lecture 3 [Arrays]

Data Structures - Lecture 3 [Arrays]

• 1.
  Arrays Muhammad Hammad Waseem m.hammad.wasim@gmail.com
• 2.
  Introduction • Arrays • Structuresof related data items • Static entity – same size throughout program 2M. Hammad Waseem
• 3.
  Arrays • Array • Groupof 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 ] 3 Name of array (Note that all elements of this array have the same name, c) Position number of the element within array c c[6] -45 6 0 72 1543 -89 0 62 -3 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] M. Hammad Waseem
• 4.
  Arrays • Array elementsare like normal variables c[ 0 ] = 3; printf( "%d", c[ 0 ] ); • Perform operations in subscript. If x equals 3 c[ 5 - 2 ] == c[ 3 ] == c[ x ] 4M. Hammad Waseem
• 5.
  Declaring Arrays • Whendeclaring arrays, specify • Name • Type of array • Number of elements arrayType arrayName[ numberOfElements ]; • Examples: int c[ 10 ]; float myArray[ 3284 ]; • Declaring multiple arrays of same type • Format similar to regular variables • Example: int b[ 100 ], x[ 27 ]; 5M. Hammad Waseem
• 6.
  Examples Using Arrays •Initializers int n[ 5 ] = { 1, 2, 3, 4, 5 }; • If not enough initializers, rightmost elements become 0 int n[ 5 ] = { 0 } • All elements 0 • If too many a syntax error is produced syntax error • C arrays have no bounds checking • If size omitted, initializers determine it int n[ ] = { 1, 2, 3, 4, 5 }; • 5 initializers, therefore 5 element array 6M. Hammad Waseem
• 7.
  Multiple-Subscripted Arrays • Multiplesubscripted arrays • Tables with rows and columns (m by n array) • Like matrices: specify row, then column 7 Row 0 Row 1 Row 2 Column 0 Column 1 Column 2 Column 3 a[ 0 ][ 0 ] a[ 1 ][ 0 ] a[ 2 ][ 0 ] a[ 0 ][ 1 ] a[ 1 ][ 1 ] a[ 2 ][ 1 ] a[ 0 ][ 2 ] a[ 1 ][ 2 ] a[ 2 ][ 2 ] a[ 0 ][ 3 ] a[ 1 ][ 3 ] a[ 2 ][ 3 ] Row subscript Array name Column subscript M. Hammad Waseem
• 8.
  Multiple-Subscripted Arrays • Initialization •int b[ 2 ][ 2 ] = { { 1, 2 }, { 3, 4 } }; • Initializers grouped by row in braces • If not enough, unspecified elements set to zero int b[ 2 ][ 2 ] = { { 1 }, { 3, 4 } }; • Referencing elements • Specify row, then column printf( "%d", b[ 0 ][ 1 ] ); 8 1 2 3 4 1 0 3 4 M. Hammad Waseem
• 9.
   2000 PrenticeHall, Inc. All rights reserved. • Initialize array • Loop • Print 9 1 2 Histogram printing program */ 3 #include <stdio.h> 4 #define SIZE 10 5 6 int main() 7 { 8 int n[ SIZE ] = { 19, 3, 15, 7, 11, 9, 13, 5, 17, 1 }; 9 int i, j; 10 11 printf( "%s%13s%17sn", "Element", "Value", "Histogram" ); 12 13 for ( i = 0; i <= SIZE - 1; i++ ) { 14 printf( "%7d%13d ", i, n[ i ]) ; 15 16 for ( j = 1; j <= n[ i ]; j++ ) /* print one bar */ 17 printf( "%c", '*' ); 18 19 printf( "n" ); 20 } 21 22 return 0; 23 } Element Value Histogram 0 19 ******************* 1 3 *** 2 15 *************** 3 7 ******* 4 11 *********** 5 9 ********* 6 13 ************* 7 5 ***** 8 17 ***************** 9 1 * • Program Output Example Program: Arrays
• 10.
  Passing Arrays toFunctions • Passing arrays • To pass an array argument to a function, specify the name of the array without any brackets int myArray[ 24 ]; myFunction( myArray, 24 ); • Array size usually passed to function • Arrays passed call-by-reference • Name of array is address of first element • Function knows where the array is stored • Modifies original memory locations • Passing array elements • Passed by call-by-value • Pass subscripted name (i.e., myArray[ 3 ]) to function 10M. Hammad Waseem
• 11.
  Passing Arrays toFunctions • Function prototype void modifyArray( int b[], int arraySize ); • Parameter names optional in prototype • int b[] could be written int [] • int arraySize could be simply int 11M. Hammad Waseem
• 12.
   2000 PrenticeHall, Inc. All rights reserved. Function definitions Pass array to a function Pass array element to a function Print 12 1 /* Fig. 6.13: fig06_13.c 2 Passing arrays and individual array elements to functions */ 3 #include <stdio.h> 4 #define SIZE 5 5 6 void modifyArray( int [], int ); /* appears strange */ 7 void modifyElement( int ); 8 9 int main() 10 { 11 int a[ SIZE ] = { 0, 1, 2, 3, 4 }, i; 12 13 printf( "Effects of passing entire array call " 14 "by reference:nnThe values of the " 15 "original array are:n" ); 16 17 for ( i = 0; i <= SIZE - 1; i++ ) 18 printf( "%3d", a[ i ] ); 19 20 printf( "n" ); 21 modifyArray( a, SIZE ); /* passed call by reference */ 22 printf( "The values of the modified array are:n" ); 23 24 for ( i = 0; i <= SIZE - 1; i++ ) 25 printf( "%3d", a[ i ] ); 26 27 printf( "nnnEffects of passing array element call " 28 "by value:nnThe value of a[3] is %dn", a[ 3 ] ); 29 modifyElement( a[ 3 ] ); 30 printf( "The value of a[ 3 ] is %dn", a[ 3 ] ); 31 return 0; 32 } Entire arrays passed call-by- reference, and can be modified Array elements passed call-by- value, and cannot be modified
• 13.
   2000 PrenticeHall, Inc. All rights reserved. Function definitions Program Output 13 33 34 void modifyArray( int b[], int size ) 35 { 36 int j; 37 38 for ( j = 0; j <= size - 1; j++ ) 39 b[ j ] *= 2; 40 } 41 42 void modifyElement( int e ) 43 { 44 printf( "Value in modifyElement is %dn", e *= 2 ); 45 } Effects of passing entire array call by reference: The values of the original array are: 0 1 2 3 4 The values of the modified array are: 0 2 4 6 8 Effects of passing array element call by value: The value of a[3] is 6 Value in modifyElement is 12 The value of a[3] is 6