Swift 'for' loop with enumerated() and zip()

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'for' loop is used every where in programming languages as the part of Control flow statements.


Consider names of few users, I have initialized them below.


let names = ["John","Fred","Maria","Rose"]


Simple for Loop
A simple 'for' loop iterating through the items is listed below.

for var i = 0; i < names.count; i++ {
    print("Name=\(names[i])")

}
This will result in compile time error in Swift 3 onwards. Below is the compile time error "C-style for statement has been removed in Swift 3"

So, lets correct it now and use a much shorter syntax.


for item in names {
    print("Name = \(item)")
}

Output:
Name = John
Name = Fred
Name = Maria

Name = Rose

for Loop with Counter
Now what if I want the counter to be also accessible within the same loop. That counter can be used to perform some operation , let's say a simple example of even or odd counter.

Using enumerated() function used with array , creates a sequence of (n,x) where n is consecutive Int starting from zero and x is the item which in this case would be a String Object.



for (index,name) in names.enumerated() {
    if index%2 == 0 {
        print ("Even Counter Assignment \(index) =>  name=\(name)")
    } else {
        print ("Odd Counter Assignment \(index) =>  name=\(name)")
    } 
}


Output:
Even Counter Assignment 0 =>  name=John
Odd Counter Assignment 1 =>  name=Fred
Even Counter Assignment 2 =>  name=Maria

Odd Counter Assignment 3 =>  name=Rose


for Loop with Index
One more simple variation where start index will be defined from 0 to any other start value.

let nameIndices = 9...12
for(i,name) in zip(nameIndices,names ) {
    print ("name=\(name) at index= \(i)")

}



 Output:
name=John at index= 9
name=Fred at index= 10
name=Maria at index= 11

name=Rose at index= 12
We can interchange the sequence parameters, meaning

zip(names,nameIndices) is valid too. Only thing changes is the sequence parameters which changes . If you notice "name" object is now first and index "i" object is the second.
for(name,i) in zip(names,nameIndices ) {
    print ("name=\(name) at index= \(i)")

}

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