lect09 array

8/6/2019 Lect09 Array

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CSIS1117 Com uter Pro rammin

1c1117 lecture 9


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Arraysrrays Initialization

Pass index variables

- - Call-by-reference

Multi-dimensional array

c1117 lecture 9 2


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,

many data items in the program for further.

E.g. Write a program to read ten numbers, then

them

i bl variables numbers in the program. It is rather troublesome.

-

. .

c1117 lecture 9 3


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int x1, x2, x3, x4, x5, x6, x7, x8, x9, x10;

cin >> x1 >> x2 >> x3 >> x4 >> x5

double mean = (x1 + x2 + x3 + x4 + x5 +

x6 + x7 + x8 + x9 + x10 / 10.0

cout


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variables variables type.

array - array purpose to form containers.

o ec are an array, we ave o spec y e ypeof the data and the maximum no. of data to bes ore .

_

char myword[31]; // storing 31 char

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array variablesarray variables,can be accessed using the subscript operator [].

const int max_no_input = 10;

= > x[i];

total += x[i];

}

double mean = total / max_no_input;cou


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,elements storing in an array with size n are

-

4

8 1

x1 x2 x3 x4 x5

variables

An array of

elements

98 4 1 0 -3 -8 6 3 -2

[0] [9][0] x[9]

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To make ro rams more readable we can use delcare

constants:

const int SIZE=10;int x[SIZE];

for (int i=0; i


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,

elements of an array can be initialized by a list of.

char choice[5];

choice[0] = 'A';

c o ce = 'B';

choice[2] = 'C';

choice[3] = 'D';

choice[4] = 'E';

= ' ' ' ' ' ' ' ' ' '

The size can be omitted if it is equal to the no. of

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ems n e s .


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char choice 5 = 'A' 'B' 'C' 'D' 'E'

cout


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sizeof(variable)izeof(variable) used to store the

variable.si eof(names) sizeof(names) array names.

sizeof(names[0])izeof(names[0]) string.sizeof(names)/size(names[0]) stringizeof(names)/size(names[0]) stringelements in the array names.

It can hel to make the ro ram more d namic.

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,

int N = sizeof(names) / sizeof(names[0]);

for(int i = 0; i < N; ++i){ ... }

The code of the for loop doesn't need to change

if the size of the array names is changed.

r e a program o rea n num ers an repor

the minimum of them. We can declare an array with size 10 to store the 10

numbers.

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Use a loo to read the 10 numbers from user

for(int i = 0; i < 10; ++i)

Traverse the array sequentially and keep the smallest

value seen so far.int min = a[0];

for(int i = 1; i < 10; ++i)

if(min > a[i]) min = a[i];

The minimum value is kept in the variablemin after thefor loop.

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accessing a non-existence element of an array.

- -

int a[5] = {2, 3, 5, 7, 11};

or n = ; ;

cout


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int p[5] = { -2, -3, -5, -7, -11 };

int q[5] = { 100, 101, 102, 103, 104 };int a[5] = { 2, 3, 5, 7, 11 };

int total = 0;

for (int i = 0; i < x; ++i){total += a[i];

cout


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array array as a simple variable in passing to a function.

,

if(x > y) return y;

return x;

You can treat it asan integer variable

}int main(){

int a 10

and pass it to thefunction smaller.

for(int i = 0; i < 10; ++i)

cin >> a[i];

n m n = a ;

for(int i = 0; i < 10; ++i)

min = smaller(min, a[i]);

c1117 lecture 9 16}


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the numbers in ascending order.

array array,the elements in the array with the smallest at the frontand the largest at the end.

How to sort the elements? Find the smallest element and ut it in the 1st entr of

the array.

Then find the 2nd

smallest element and put it in the 2nd

entry

Until the end, the largest element is put in the last entry.

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Take the 10 numbers from input and store them in an array

98 4 1 7 2 0 6 5 3

a[0] a[9][0] a[9]Scan the array one time and find the smallest

a[0] a[9]98 4 1 7 2 0 6 5 3

Swap this smallest element with the first element

a[0] a[9]

90 4 1 7 2 8 6 5 3

a[0] a[9]c1117 lecture 9 18

a[0] a[9]


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Similarly, find the 2nd smallest element byscanning the array once

a[0] a[9]

Swap it with the element in the 2nd entry of the array

90 2 1 7 4 8 6 5 3

[0] [9][0] a[9]

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Until the lar est element is ut at the end of the arra

30 1 2 4 5 6 7 8 9

The elements in the array are sorted, and we only

a[0] a[9].

How we can sort the elements in ro rams? It can be done by using nested loops.

Outer loop: scan from i=0 to 9, the i-th iteration locatethe i-th smallest element and put it in the i-th entry.

Inner loop: scan the array to locate the i-th smallestc1117 lecture 9 20

.


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index uses to store the index of the i-th smallest

for(int i = 0; i < 10; ++i){

element in the i-th iteration.

int index = i;

for(int j = i + 1; j < 10; ++j)

a n ex a

index = j;

int temp = a[index];Scan the array from the(i+1)-th elements to the last

a[index] = a[i];

a[i] = temp;

one in the i-th iteration andupdate the variable index if

Swap the i-th smallest elementvalue among them.

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with the element in i-th entry


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function function used in the previous program

exchange their values in the array.

Exchange thea[0] a[9]98 4 1 7 2 0 6 5 3

e ement inposition 0 withswap(a[0], a[6])

a[0] a[9]

position 6.

a[0] a[9]90 4 1 7 2 8 6 5 3

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a[0] a[9]


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void swap(int p, int q){

p = q;

q = temp;

}

int x = 10; int y = 20;

cout


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- -

The variables x and are called value arameters.

For value parameter, the argument is copied into the

memor that belon s to the arameter. An chan esof the value are only valid to the parameter variablebut not the argument.

void swap(int x, int y){

int tem = x

x10

x = y;

y = temp;

swap(x, y);

c1117 lecture 9 24Main memory


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int tem =

x10

p = q;

q = temp;

swa x

20 q

Main memory

When the swap function is called, the values ofvariables x and y are copied to the local variables

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.


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int tem =

x10

p = q;

q = temp;

swa x

10

tem

q10

Main memory

Inside the swap function, only the local variables areupdated but not x and y. The values ofx and y are not

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.


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- -

For reference parameter, the argument is the memory,.

For referencing the memory address of a variable, we add

void swap(int&p, int& q){

=

.

p = q;

q = temp;

An argument for a referent parameter should be a

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var a e, see roots.cc as an examp e.


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void swap(int& p, int& q){

int tem = x p = q;

q = temp;y20 , q

swa x

i blMain memory

en t e swap unct on s ca e , t e oca variablespand q are pointing to the same memory locations ofx

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. .


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void swap(int& p, int& q){

p = q;

q = temp;

}

int x = 10; int y = 20;

cout


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array array functions? Array in ++ n nl functionsrray functions

reference. Usually the size of an array is also passed explicitly by

caller. We do not need to add & before the array variable.void print_array(int a[], int size){

for(int i = 0; i < size; ++i)cout


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void sorting(int x[], int size){

or nt = ; < s ze; ++

int index = i;

for(int j = i + 1; j < size; ++j)if(x[index] > x[j])

index = j;

,

}print_array(x,10);int main(){

} int a[10];

for(int i = 0; i < 10; ++i)

>>sorting(a, 10);

return 0;

as the argument

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int main

a3

int a[10];

for(int i = 0; i < 10; ++i)8

21c n >> a ;

sorting(a, 10);return 0;

-10

}

-32

10 3 4 8 21 1 0 9 32 2

c1117 lecture 9 32Main memory


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void sorting(int x[],int size){

for(int i=0; i


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void sorting(int x[],int size){

for(int i=0; i


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-

array array , , indexes. We call these kinds of arrays Multi-

.

A2D array is just an array of array.

int mytable[3][8];// A table with 3 rows and 8 columns

2D arrays are useful to implement table-like data

, . . .

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Column

Mytable[0][0]my a e

Row

Mytable[1][4]ytable[1][4]Mytable[2][7]

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- ,have bounds for all dimensions except the first one.

int mytable[][3] = { {1, 0, 4}, {-1, 1, 2}};

Same rule apply to pass argument in functions.vo pr nt_mu t array nt a , nt s ze

for(int i = 0; i < size; ++i)

=

lect09 array

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