swift - Difference between 'for index' and traditional 'for loop' -

i'm new swift , pretty new programming. i'm not sure if it's because it's 2:34 can me identify difference between these 2 loops?

the first 1 resulting in values want yet uses (as swift documentation explains) 'traditional c loop' 1 after using seems swift preferred 'for index' loop (which clearer me), problem loop returns every number rather meeting conditional.

func findlargestprimefactor(number: int) {     var = 2; < number; += {         if number/i % 1 > 0 {          } else {             print(i);         }     } }  findlargestprimefactor(13195); 

below returning every number 13195

func findlargestprimefactor(number: int) {     in 2...number {         if number/i % 1 > 0 {          } else {             print(i);         }     } }  findlargestprimefactor(13195); 

i've realised how stupid mistakes were, first of have no idea why doing += i, didn't make sense @ all.

also, conditional never being met because declared int when needed float because care remainders!

edit: i've updated code yet again (taken everyones feedback consideration), feel bit better , continue working on solution.

thanks help!

updated code

func findlargestprimefactor(number: int) {     in 2...number {         var n = float(number)         var count = float(i)             if n/count % 1 > 0 {                 print("not divisible")             } else {             print(i)         }     } }  findlargestprimefactor(13195);