Register
an account, download Xcode.
Open
Xcode, File > New > Playground, enter a name, screen look like this
We code on
left panel, on right, Xcode auto run to show result. You can press triangle
blue button at bottom left to make it run immediately.
Copy in to
playground.
let str2="First string"
var concat=str+str2
We call str, str2,
concat are variables, the line var str=”Hello, playground”
declare a variable.
Let mean constant, we
can’t assign or change value like var.
Type continue
str2="next"
An red mark appear, move
cursor to it, Xcode say can’t assign value to str2, need change to var, double
click to fix it, let str2 will change to var str2.
Continue.
let a=8
let b=10
var sum=a+b
Xcode auto recognize
data type, we always use let or var for any data type.
Type two cross before
line var tong=a+b, it become comment.
We comment
to know what we did, next day easy to remember.
Continue
let text=”8”
let sum=b+text
Xcode show
error mark because text is String, can’t sum with integer.
All
characters in quotation mark will be consider as String.
To change
a String to number, we use:
let number=Int(String)
Copy to continue.
if(a>b){
sum=10
}
else{
sum=100
}
Run to see
result 100.
Now delete else command,
run, screen show 18.
We see the different of if has else
and no else.
If has else, when if not true,
command go to else, value will be 100. I no else, age still remain value 27,
value of a+b.
Continue.
var c=0
for i in0..<5 {
c=c+i
}
c
Xcode show result 5
times and number 10. For loop use to repeat a command, here we sum number from
0 to 5.
Add if
command in to for.
if(i%2==0)
Character % % character
mean divide and get remainder.
We sum all
even numbers from 0-5.
Result
equalt 6, which mean 2 + 4.
Change to if(i%2==1), result equalt 4,
mean 1 + 3.
Here if has
no else, because we don’t care about other numbers.
Continue
var d=1.8
var e=d/7
Run too
see decimal number.
More
practical with * and /
Excercise
Use for loop to sum even or odd number from 1-100.
No comments:
Post a Comment