Lecture 25: Multi-Dimensional Arrays

LECTURE 25: MULTI-DIMENSIONAL ARRAYS

CSC 107 – Programming For Science

Today’s Goal

Get familiar with multi-dimensional arrays Creating variables for multi-dimensional

array Multi-dimensional array entry assignments Using values stored in the entries in these

Problem with Variables

Normal variable has single value at any time Can do better & hold list of values in an array

Only 1 value per entry, however, & size is fixed But this is very limiting in most situations

Bar codes are boring pictures

Must evaluate bridge stresses in multiple dimensions

Cannot do this with what we have so far

Multi-dimensional Arrays

Multiple dimensions refine how data viewed 1-d array is a row of data

Create an entire table of entries with 2-d array

3-d array creates box of entries

Each entry still holds one piece of data Column used in 1-d array to access

column Access entries in 2-d array with row &

column 17 indices needed for entry in 17-dimension

array Using an entry still depends on array

variable Values are independent of all other entries Its all about the values: only work with

single entry

Declaring Arrays Variables

Like all variables, must declare before use

Type, name, & size of each dimension needed Each of the array's entries hold value of

that type Size must be integer since ½ a value hard

to useint prettyPicture[256][32];float armada[MAX_SHIPS][MAX_DECKS];double taxesOwed[MAX_EARN][10];char names[17][MAX_NAME_SIZE];long number[1][1];

Working With Arrays

0 is start of columns, rows, (& everything else) Within table, all rows have same number of

columns Identical rows & columns in 3-d array on z-

dimension Still cannot find size of array on any

dimension Even finding number of rows or columns

impossible Still no warning exceeding bounds of

array But restricts code to use entry or array

variable Entire row or column cannot be used in any

Initializing an Array

Declare array variable and set initial values

All entries must have initial value specified Starts with open brace… … open brace & values for row’s entries… …finally add a closing brace to end row… …closing brace to end the initializationdouble switch[2][2] ={{0,1},{2.2,3.2}};char epoch[3][1] = {{‘A’},{‘B’},{‘C’}};int dozer[1][1] = {{1}};bool raygun[3][3] = {{true,false,true}};

Using An Array

Each entry used like variable as normal But only can entry via array variable Use brackets for each dimension to identify

the entry Multidimensional arrays ♥ for loops,

tooint picture[20][10];for (int i = 0; i < 20; i++) { for (int j = 0; j < 10; j++) { picture[i][j] = (i * 10) + j; }}

Multi-Dim. Array Example

float bridgeStress[100][100];int times[100];

bridgeStress[0,4] = 3.5;times[45] = 2;bridgeStress(23)(12) = pow(12, 2);times[12] = times[45] * 4;bridgeStress[2] += times[12];times[99] = bridgeStress[0][34] + 34;bridgeStress[3][12] = times[-2];bridgeStress[2][0] = 0;bridgeStress[2][0] += 45;bridgeStress[3][2] = pow(2,bridgeStress[2][0]);

Passing an Array

Entry like any variable & can pass to function Value of the entry cannot change in

function Entry's current value received by the

functionfabs(values[8][4]);cos(momentum[4][1]);

Pass entire array as argument for a function As before, parameter must be array of

same type Must specify number of columns in the

parameter

Working With 2d Parameters

int determinant(int a[][2]) { return (a[0][0]*a[1][1])–(a[1][0]*a[0][1]);}\int main(void) { int bookExample[2][2]; bookExample[0][0] = 1; bookExample[0][1] = 3; bookExample[1][0] = -1; bookExample[1][1] = 5; int det = determinant(bookExample); cout << det;}

Your Turn

Get into your groups and try this assignment

For Next Lecture

Arrays & arrows discussed in Sections 12.1 – 12.5 We used arrows in a trace; but how do they

work? * not used enough; where else can I use it in

program? Can C++ make it even easier to shoot

ourselves in foot?

Angel also has Weekly Assignment #9 due Tues.

Programming Assignment #2 due in one week

Lecture 25: Multi-Dimensional Arrays

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