gistfile1.m

//NumberParser.h
@interface NumberParser : NSObject
{
	char *str;
}

-(void)addDigit:(char)ch;
-(double)doubleValue;

@end
//NumberParser.m
#include <stdlib.h>
#include <string.h>

@implementation NumberParser
-(void)addDigit:(char)ch{
	if(str){
		size_t len=strlen(str);
		str=realloc(str,len+2);
		str[len]=ch;
		str[len+1]='\0';
	}else{
		str=calloc(2,sizeof(char));
		*str=ch;
	}
}

-(double)doubleValue{
	double num=atof(str);
	free(str);
	str=NULL;
}

@end