Lesson 2 - Array, String

Array is a set of values with same data type.

Array of number.

let data = [1, 2,3, 4,5]

Array of string.

let data2 = ["Monday","Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday" ]

var array = [String](count: 12, repeatedValue: " ")

var array2 = [Int](count: 12, repeatedValue: 0)

We declare array contain 12 String elements, array2 contain 12 integer elements.

To add more elements, we use append

array.append("Monday");

array2.append(9);

To get array size

let size=data.count

Use for to sum all odd number in data.

for i in 0..<5 {

if(data[i]%2==1){

sum=sum+data[i]

    }

}

Run to see result 9.

Care about array index, first element will be array[0], last elements will be array[size-1]

sum=sum+data[i] mean sum previous value with current value.

You can also write it like this sum+=data[i]

Add to data numbers 35,88.

If we want to know position of number 35 in ar array, use for like this.

int index=0;

for i in0..<data.count {

if(data[i]==35){

index=i+1

    }

}

Value equal 6, plus 1 because i=0 mean first elements.

We want to count how many even number in array ar2.

var count=0

for i in0..<data.count {

if(data[i]%2==0){

count=count+1

    }

}

We want to print max number in data, copy these lines.

var max=data[0]

for i in0..<data.count {

if(data[i]>max){

max=data[i]

    }

}

Result is 88.

Next to two dimension array, we declare like this.

let array3  = [[1, 2, 3, 4, 5],[1, 2, 3, 4, 5]]

Now array has 2 rows, 5 column, elements look like this

1  2  3  4  5 

1  2  3  4  5 

Element at row 2, column 3 will be write array3[1][2], it is number 3.

We also can declare like this.

var array4 = Array(count: 2, repeatedValue:Array(count:3,repeatedValue: 0))

Array will has two row, 3 column.

We add value like this

array4[0][0]=4

array4[0][1]=8

array4[0][2]=6

array4[1][0]=5

array4[1][1]=9

mang4[1][2]=3

Elements now look like this

4 8 6

5 9 3

To sum all elements in array4, we use double for loop.

var sum2=0

for i in0..<2 {

for j in0..<3 {

sum2=sum2+array4[i][j]

}

}

Result is 35.

To understand double for loop, think like this:

First, i=0, run for below with j from 0 to 2

Next, i=1, run for with j from 0 to 2

That mean we run single for with j in i times. Here i mean number of row, i=0 is first row, i=1 is second row.

Repeat single for mean double for loop, you should understand it in practical.

Next to string character.

We need to know about split string.

For example, we have a string like this.

let a="This is example text, we will split by comma";

We create an array by split string like this.

let array5 = a.componentsSeparatedByString(",")

Array5 now has 2 elelents "This is example text”, “ we will split by comma"

To remove blank character in “ we will split by comma"

let remo=array5[1].characters.dropFirst()

let string2=String(remo)

To count number of chacracter, use characters.count

Blank chacracter is counted as one character.

We frequently split String to array when make app.