Question

I am puzzled by why the output is not what I expect it to be in the following nested while loops:

i = 1
j = 1
while(i<5){
 print("i")
 print(i)
 i = i + 1
 while(j<5){
  print("j")
  print(j)
  j = j + 1
 }
}

The output I get is:

[1] "i"
[1] 1
[1] "j"
[1] 1
[1] "j"
[1] 2
[1] "j"
[1] 3
[1] "j"
[1] 4
[1] "i"
[1] 2
[1] "i"
[1] 3
[1] "i"
[1] 4

But I was expecting something along the lines of

[1] "i"
[1] 1
[1] "j"
[1] 1
[1] "j"
[1] 2
[1] "j"
[1] 3
[1] "j"
[1] 4
[1] "i"
[1] 2
[1] "j"
[1] 1
[1] "j"
[1] 2
[1] "j"
[1] 3
[1] "j"
[1] 4
...

Any suggestions? Thank you for your help.

Answer 1

There’s nothing wrong about the loop’s behavior.

i = 1 // Beginning of your code, you're initializing i, changing its value to 1
j = 1 // ... initializing j as well.
while(i<5){   // looping while i < 5
 print("i")
 print(i)
 i = i + 1    // incrementing i
 while(j<5){  // looping while j is < 5
  print("j")
  print(j)
  j = j + 1   // incrementing j
 }
}

Now think a little bit more about your code.

What you want is your second while loop to actually loop 4 times for each loop of the first one.

So you’re expecting j‘s value to be set back to 1 inside the scope of the first while loop, magically? You might want to try doing it yourself, don’t you?