chapter 8 - two dimensional arrays

7/24/2019 Chapter 8 - Two Dimensional Arrays

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Copyright © 2012 Pearson Education, Inc.

Chapter 8

Two Dimensiona !rrays



2Copyright © 2012 Pearson Education, Inc.

"utine

"#$ecti%es1.Two Dimensiona !rrays

2.&atrices

De%eop pro#em soutions in C''containing(

) &atri* computations

) Input +rom Data ies) unctions to Compute -ums and !%erages



Two Dimensiona !rrays

) Decaration and Initiai/ation

) Computation and "utput) unction !rguments




Two Dimensiona !rrays) ! two dimensiona array stores data as a

ogica coection o+ rows and columns.

) Each eement o+ a twodimensiona array has a row

position and a coumn position.

) To access an eement in a twodimensiona array,

you must speci+y the name o+ the array +oowed #y(

a row offset

a column offset




3

Decaration and Initiai/ation) The decaration o+ a twodimensiona array re4uires a row

size and a column size.

) ! consecuti%e #oc5 o+ 6row size76column size7 memory

ocations are aocated.

) ! array eements must #e o+ the same type.

) Eements accessed #y two o++sets a row o++set and a

coumn o++set.

) The name o+ the array hods the address o+ the +irst #yte o+

memory




9

E*ampe//Declaration

int data[2][3];

Eements can #e accessed in the same way as accessing the eements 1D array


Memory Snapshot

:

:

::

:

:

data


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E*ampe

//Declaration

int data[2][3];


? ? ?

? ? ?

row 0

row 1

col 0 col 1 col 2

row/column form:



2D !rray De+inition -ynta*


Syntax:data<type identi+ier [ =row<si/e> ][coumn<si/e] == initiai/ation<ist >;??row<si/e and coumn<si/e must #e integer constants

E*ampesint data[2][5]; //allocates consecutive memory for 10 integer valuesdouble t[2][2] = {{30!50"!{21!#2""; //allocates and initiali$es

@aid Ae+erencescout %% data[1][3];cout %% t[1][0];

In%aid Ae+erencescout %% data[2][5]; //invalid offset

cout %% t[&1][&1]; //invalid offset


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Initiai/ation E*ampes

int tem'[(][3] = {50! #0! )0! (*! #5!)2! 51! )+! )0! 52! #*! )3";

int tem'[(][3] = {{50! #0! )0"! {(*! #5! )2"!

{51! )+! )0"! {52! #*! )3"";

int t2[#][(] = {{50! #0! )0"! {(*! #5! )2"!

{51! )+! )0"! {52! #*! )3"";

int tem'[][3] = {{50! #0! )0"! {(*! #5! )2"!

{51! )+! )0"! {52! #*! )3"";int tem'[][3] = {50! #0! )0! (*! #5! )2! 51!

)+! )0! 52! #*! )3";




E*ampe( Input sing cin) ested for oops are o+ten used when

inputting and assigning %aues to a twodimensiona array. ested oops are generay use+u +or getting around the 2D

arrays


//Declarationdouble table[,-.][-.];

for int i=0; i%,-.; i4 //every ro for int 6=0; 6%-.; 6 4//every col cin 77 table[i][6];



11

E*ampe( !ssignment


//Declarationconst int ,-.34!-.24;double v[,-.][-.];

for int i=0; i%,-.; i4 //every ro for int 6=0; 6%-.; 6 4//every col v[i][6] = i6;

0 1

1 2

2

V



12

E*ampe( Computations) Compute the a%erage %aue o+ an array

with n rows and m coumns.


double sum04! average;for int i=0; i%n; i4 //every ro for int 6=0; 6%m; 6 4//every col sum = array[i][6];

average = sum / n8m4;



1

E*ampe( Computations

) Compute the a%erage %aue o+ the nth row

o+ a 2D array with r rows and c coumns.


double sum04! ro9verage;for int 6=0; 6%c; 6 4 //every col sum = array[n][6];

average = sum / c;



1

&odi+yF

) &odi+y the C'' statements on the

pre%ious side to compute the a%erage o+

the mth coumn.




13

"utputting 2D !rrays

) Two dimensiona arrays are o+ten printed in

a row #y row +ormat, using nested for

statements.

) Ghen printing the row %aues o+ an array,

#e sure to print(

whitespace #etween the %aues in a row. a newine character at the end o+ each row.




19

E*ampe( Printing


for int i=0; i%n; i4 {//every ro for int 6=0; 6%m; 6 4//every col

cout %% array[i][6] %% : :; cout %% endl; //add end&of&line eacro"



1;

2D !rrays as unction Parameters

) 2D arrays are aways passed #y re+erence.

) The coumn dimension must #e speci+ied. The e+tmost

dimension 6row7 may #e empty =>.

) unction prototype e*ampe(

int row!%erage6int Arr[][COLSIZE] int whichAow7H) !rray decaration in main(

int ta!le ["O#SIZE][COLSIZE];

) unction in%ocation e*ampe(

a%g row!%erage6ta!le, 7H




18

Documentation -tye) Gedocumented +unctions aways

incude preconditions and postconditions in the+unctionJs comment header #oc5.

Preconditions descri#e the conditions assumed to #e

true at the time the +unction is caed.) I+ preconditions are not met, there is no guarantee that the

+unction wi wor5 correcty.

Postconditions descri#e the changes that wi #e

made to the arguments during the e*ecution o+ the

+unction.




1B

&atri*) ! matri* is a set o+ num#ers arranged

in a rectanguar grid with rows and coumns.

) ! s4uare matri* has the same num#er o+ rows

as coumns.

) Aow and Coumn o++sets in &atrices are 1

#ased.

) 2D !rrays are use+u +or representing matrices. Aemem#er that C'' uses 0#ased o++setsF




20

&atri* Computations and "perations) The determinant o+ a matri* is a scaar %aue used

in computing matri* in%erses and so%ing systems o+

simutaneous e4uations.

) The transpose o+ a matri* is a new matri* in which the rows o+

the origina matri* are the coumns o+ the transpose.

) &atrices o+ the same si/e may #e added or su#tracted eement

#yeement.

) &atri* mutipication 6& 7 is de+ined ony when the num#er o+

coumns o+ & is e4ua to the num#er o+ rows in . Aesut has the si/e rows6&7 * cos67




21

E*ampe sing 2D !rrays

Kincude LiostreamMKincude Lcstdi#Musing namespace stdHint main67N ?? decare the matrices(

int mat1=>=>, mat2=>=>, add=>=>H??generate the matrices(+or 6int i0H iLH i''7 +or 6int $0H $LH $''7 N mat1=i>=$>rand67O100H ??assume a eements ess than 100 mat2=i>=$>rand67O30H ??assume a eements ess than 30 ??add the matrices(+or 6int i0H iLH i''7 N +or 6int $0H $LH $''7N res=i>=$>mat1=i>=$>'mat1=i>=$>H

cout LL res=i>=$> LLQ QH cout LL endH

return 0H

Write C++ program to randomly generate two 4x4 matrices and addthem into a new matrix?

Possi#e output(

101 0 210 110 20 111 3;

1 2 110

80 3 220 8;



22

E*ercise sing 2D !rrays

Write C++ program to generate two 4x4 matrices

randomly and multiply them?

REMEMBER: The result of multiplication will be a 4x4

matrix as well.

chapter 8 - two dimensional arrays

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