changing output in objective-c app

Question

This is supposed to decrypt a hex string with an ascii string, using rc4 decryption. I'm converting my java application to objective-c. The output keeps changing, every time i run it.

#import "RC4.h"
@implementation RC4

@synthesize txtLyrics;
@synthesize sbox;
@synthesize mykey;

- (IBAction) clicked: (id) sender
{
 NSData *asciidata1 = [@"4875" dataUsingEncoding:NSASCIIStringEncoding allowLossyConversion:YES];
 NSString *asciistr1 = [[NSString alloc] initWithData:asciidata1 encoding:NSASCIIStringEncoding]; //[txtLyrics setText:@"go"];
 NSData *asciidata = [@"sdf883jsdf22" dataUsingEncoding:NSASCIIStringEncoding allowLossyConversion:YES];
 NSString *asciistr = [[NSString alloc] initWithData:asciidata encoding:NSASCIIStringEncoding]; //RC4 * x = [RC4 alloc];
 [txtLyrics setText:[self decrypt:asciistr1 andKey:asciistr]];
}

- (NSMutableArray*) hexToChars: (NSString*) hex
{
 NSMutableArray * arr = [[NSMutableArray alloc] init];
 NSRange range;
 range.length = 2;
 for (int i = 0; i < [hex length]; i = i + 2)
 {
  range.location = 0;
  NSString * str = [[hex substringWithRange:range] uppercaseString];
  unsigned int value;
  [[NSScanner scannerWithString:str] scanHexInt:&value];
  [arr addObject:[[NSNumber alloc] initWithInt:(int)value]];
 }
 return arr;
}
- (NSString*) charsToStr: (NSMutableArray*) chars
{
 NSString * str = @"";
 for (int i = 0; i < [chars count]; i++)
 {
  str = [NSString stringWithFormat:@"%@%@",[NSString stringWithFormat:@"%c", [chars objectAtIndex:i]],str];
 }
 return str;
}

//perfect except memory leaks
- (NSMutableArray*) strToChars: (NSString*) str
{
 NSData *asciidata = [str dataUsingEncoding:NSASCIIStringEncoding allowLossyConversion:YES];
 NSString *asciistr = [[NSString alloc] initWithData:asciidata encoding:NSASCIIStringEncoding];
 NSMutableArray * arr = [[NSMutableArray alloc] init];
 for (int i = 0; i < [str length]; i++)
 {
  [arr addObject:[[NSNumber alloc] initWithInt:(int)[asciistr characterAtIndex:i]]];
 }
 return arr;
}

- (void) initialize: (NSMutableArray*) pwd
{
 sbox = [[NSMutableArray alloc] init];
 mykey = [[NSMutableArray alloc] init];
 int a = 0;
 int b;
 int c = [pwd count];
 int d = 0;
 while (d < 256)
 {
  [mykey addObject:[pwd objectAtIndex:(d % c)]];
  [sbox addObject:[[NSNumber alloc] initWithInt:d]];
  d++;
 }
 d = 0;
 while (d < 256)
 {
  a = (a + [[sbox objectAtIndex:d] intValue] + [[mykey objectAtIndex:d] intValue]) % 256;
  b = [[sbox objectAtIndex:d] intValue];
  [sbox replaceObjectAtIndex:d withObject:[sbox objectAtIndex:a]];
  [sbox replaceObjectAtIndex:a withObject:[[NSNumber alloc] initWithInt:b]];
  d++;
 }
}
- (NSMutableArray*) calculate: (NSMutableArray*) plaintxt andPsw: (NSMutableArray*) psw
{
 [self initialize:psw];
 int a = 0;
 int b = 0;
 NSMutableArray * c = [[NSMutableArray alloc] init];
 int d;
 int e;
 int f;
 int g = 0;
 while (g < [plaintxt count])
 {
  a = (a + 1) % 256;
  b = (b + [[sbox objectAtIndex:a] intValue]) % 256;
  e = [[sbox objectAtIndex:a] intValue];
  [sbox replaceObjectAtIndex:a withObject:[sbox objectAtIndex:b]];
  [sbox replaceObjectAtIndex:b  withObject:[[NSNumber alloc] initWithInt:e]];
  int h = ([[sbox objectAtIndex:a]intValue] + [[sbox objectAtIndex:b]intValue]) % 256;
  d = [[sbox objectAtIndex:h] intValue];
  f = [[plaintxt objectAtIndex:g] intValue] ^ d;
  [c addObject:[[NSNumber alloc] initWithInt:f]];
  g++;
 }
 return c;
}
- (NSString*) decrypt: (NSString*) src andKey: (NSString*) key
{
 NSMutableArray * plaintxt = [self hexToChars:src];
 NSMutableArray * psw = [self strToChars:key];
 NSMutableArray * chars = [self calculate:plaintxt andPsw:psw];
 NSData *asciidata = [[self charsToStr:chars] dataUsingEncoding:NSASCIIStringEncoding allowLossyConversion:YES];
 NSString *asciistr = [[NSString alloc] initWithData:asciidata encoding:NSUTF8StringEncoding];
 return asciistr;
}

@end