Ive seen other examples and tried

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string

I am not sure what I am doing wrong, I just started coding my first Iphone App

This is what I am trying to do

I have 4 textfields and each has a limit on number of letters while typing I have done this using the below code

- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
{
int valid;
    NSString *cs2 = [textField.text stringByReplacingCharactersInRange:range withString:string];
//    int charCount = [cs2 length];

    if(textField == cvv){
        valid = 4;
    }else if(textField == cardName) {
        valid=26;
    }else if(textField == expDate) {
        valid=5;

//        if (charCount == 2 ) {
//            textField.text = [cs2 stringByAppendingString:@"/"];
//            textField.text = cs2; 
//            return YES;
//        }



    }else if(textField == acNumber) {
        valid=19;
    }


    return !([cs2 length] > valid);

Works fine till here, I have a textfield where the user enters Exp date and would like to format it as if I am entering 112 then it should display as 01/12 and if I enter 2 then it should display as 1122

I tried checking if the length of the textfield value is 2 then append a / but then that gives me when I enter 12 it gives 11/22