得到子字符串出现的次数

    NSString *str=@"12231354654656";

    

    NSUInteger cnt = 0, length = [str length];

    NSRange range = NSMakeRange(0, length);

    while(range.location != NSNotFound)

    {

        range = [str rangeOfString: @"65" options:0 range:range];

        if(range.location != NSNotFound)

        {

            range = NSMakeRange(range.location + range.length, length - (range.location + range.length));

            cnt++; 

        }

    }