Adding Thousands Separator commas to a number manually without using NSNumber formatting method

NSString+NumberMethods.h

//
//  NSStringCategory.h
//  AdamoCalc
//
//  Created by Tanapon Petapanpiboon on 10/11/11.
//  Copyright 2011 toptanapon@gmail.com. All rights reserved.
//

#import <Foundation/Foundation.h>

@interface NSString(NumberMethods)

-(NSString *)stringWithThousandsSeparator;
-(NSString *)numberStringWithFormat;
-(NSString *)numberStringByRemovingFormat;
-(int)digitCount;
-(NSString *)numberStringByRemovingTrailingZeros;
-(NSString *)numberStringWithLimitedDigits;

@end

NSString+NumberMethods.m

//
//  NSStringCategory.m
//  AdamoCalc
//
//  Created by Tanapon Petapanpiboon on 10/11/11.
//  Copyright 2011 toptanapon@gmail.com. All rights reserved.
//

#import "NSStringCategory.h"

@implementation NSString(NumberMethods)

//This is a simple version for adding a thousands separator comma
-(NSString *)stringWithThousandsSeparator
{
    int l = [self length];
    int a = l/3;
    int b = l%3;
    int x = (((a-1)*3)+b);
    
    NSMutableString *mutableString = [self mutableCopy];
    
    if (x>0) {
        x=x+3;
        do {
            x=x-3;
            [mutableString insertString:@"," atIndex:x];
            //NSLog(@"%i",x);
        } while (x>3); 
    }
    self = [NSString stringWithString: mutableString];
    [mutableString release];
    return self;
}

//Removes ,
-(NSString *)numberStringByRemovingFormat
{
    return [self stringByReplacingOccurrencesOfString:@"," withString:@""];
}

//This one is used in Adamo Calculator
//Supports 1000, -1000, 1000.01, -1000.01
-(NSString *)numberStringWithFormat
{
    if (![self isEqualToString:@"Error"]) {
        NSMutableString *beforeString = nil;
        NSString *afterString = nil;
        BOOL isNegative = [self rangeOfString:@"-"].location != NSNotFound;
        NSLog(@"Before:%@",self);
        if (isNegative) {
            self = [self stringByReplacingOccurrencesOfString:@"-" withString:@""];
            NSLog(@"After:%@",self);
        }
        if ([self rangeOfString:@"."].location == NSNotFound) {
            beforeString = [self mutableCopy];
        } else {
            NSArray *stringComponents = [self componentsSeparatedByString:@"."];
            beforeString = [[stringComponents objectAtIndex:0] mutableCopy];
            afterString = [stringComponents objectAtIndex:1];
        }
        
        NSLog(@"beforeString:%@",beforeString);
        
        int l = [beforeString length];
        int a = l/3;
        int b = l%3;
        int x = (((a-1)*3)+b);
        
        if (x>0) {
            x=x+3;
            do {
                x=x-3;
                [beforeString insertString:@"," atIndex:x];
                //NSLog(@"%i",x);
            } while (x>3); 
        }
        if (afterString) {
            self = [NSString stringWithFormat:@"%@%@%@",beforeString,@".",afterString];
        } else {
            self = [NSString stringWithString:beforeString];
        }
        //NSLog(@"%@",self);
        
        if (isNegative) {
            self = [NSString stringWithFormat:@"-%@",self];
        }
        
        [beforeString release];
    }
    return self;
}

//Counts digits without . or -
-(int)digitCount
{
    return [[[[self stringByReplacingOccurrencesOfString:@"," withString:@""] stringByReplacingOccurrencesOfString:@"." withString:@""] stringByReplacingOccurrencesOfString:@"-" withString:@""] length];
}

//Removes decimal trailing zeros
-(NSString *)numberStringByRemovingTrailingZeros
{
    BOOL isDecimal = [self rangeOfString:@"."].location != NSNotFound;
    if (isDecimal) {
        int index = (int)[self length] - 1;
        BOOL trim = NO;
        while (([self characterAtIndex:index] == 48 || [self characterAtIndex:index] == 46) && index>0) { // (0 or .)
            //If the last character is a dot @".", exit function afterwards
            if ([self characterAtIndex:index] == 46) {
                index--;
                trim = YES;
                break;
            }
            index--;
            trim = YES;
        }
        if (trim) {
            self = [self substringToIndex:index + 1];
        }
    }
    return self;
}

//The number string passed to this method, must not have commas. Call numberStringByRemovingFormat first.
-(NSString *)numberStringWithLimitedDigits
{
    //If int value is more than 999,999,999, or if the string is "nan" (by 0 / 0)
    if ([self intValue] > kMaximumAmountAllowed || [self intValue] < kMaximumAmountAllowed*-1 || [self isEqualToString:@"nan"] || [self isEqualToString:@"inf"]) {
        self = @"Error";
    } else {
        int length = (int)[self length];
        int maximumDigits = kMaximumDigitsAllowed;
        int index = length - 1;
        BOOL trim = NO;
    
        //If a . (dot) is found, index++
        if ([self rangeOfString:@"."].location != NSNotFound) {
            index++;
        }
        
        //If a - (negative) is found, maximumDigits++
        if ([self rangeOfString:@"-"].location != NSNotFound) {
            maximumDigits++;
        }
        
        //as long as length is over maximum digits allowed
        while (length > maximumDigits) {
            index--;
            length--;
            //if the last char is a (.), index--
            if ([self characterAtIndex:index] == 46) {
                index--;
            }
            trim = YES;
        }
        if (trim) {
            self = [self substringToIndex:index +1];
        }
    }
    return self;
}

@end