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ft_atoi.c
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ft_atoi.c
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/* ************************************************************************** */
/* */
/* ::: :::::::: */
/* ft_atoi.c :+: :+: :+: */
/* +:+ +:+ +:+ */
/* By: pbie <marvin@42.fr> +#+ +:+ +#+ */
/* +#+#+#+#+#+ +#+ */
/* Created: 2015/11/24 20:01:57 by pbie #+# #+# */
/* Updated: 2015/12/03 17:18:25 by pbie ### ########.fr */
/* */
/* ************************************************************************** */
#include "libft.h"
/*This is a recreation of the atoi function in C. We take a string of
* characters that are supposed to be a number converted into an int.
* According to the man, "The atoi function converts the initial portion of
* the string point to by str to int representation."*/
int ft_atoi(const char *str)
{
/*We start off by creating three variables. The first is what will hold our
* result that is to be returned. We use long because it is guaranteed to
* be able to store, at the very least, values that lie within the range of
* -2147483647 and 2147483647. Sign will be what we use to turn the int
* negative in the event that its a negative number that is put in the
* string. We have it as a long so we can multiply our result by it in the
* end. We next have an unsigned int i, which will be the counter for our
* string. In order to be able to compensate for an incredibly long string
* we use an unsigned int to be able to use its extended positive range it
* has over a signed int. We will set all of them to 0 except for our sign
* which we set at 1 to use based based on the appearance of a negative
* symbol in our string*/
long res;
long sign;
unsigned int i;
res = 0;
sign = 1;
i = 0;
/*The first thing we want our function to do is make sure to skip over any
*kind of spacing that could be found at the beginning of the string.*/
while (str[i] == ' ' || str[i] == '\t' || str[i] == '\n' ||
str[i] == '\r' || str[i] == '\v' || str[i] == '\f')
i++;
/*Once past the extra spacing, if it exists, we are checking to see if there
*is a negative symbol at the beginning of the number we will be converting.
if we see a negative symbol or a positive symbol we adjust accordingly. If
it's negative we set our sign equal to -1 to multiply to our result when
we return it.*/
if (str[i] == '-' || str[i] == '+')
{
if (str[i] == '-')
sign = -1;
i++;
}
/*Here we convert our string of characters from char to int so long as they
* are numbers. If the character we are currently on is a number, we
* converted it to its ascii numerical value. For the first character res
* is always set currently at 0. We multiply 10 immediately by our res to
* set up the digit placement where it should be. We then subtract the
* numerical value of the character 0 on the ascii table from our currently
* character number. This sets it to its ascii numerical value. We then
* start our loop over and continue until we hit a character that is not a
* number.*/
while (str[i] >= '0' && str[i] <= '9')
{
res = res * 10 + str[i] - '0';
i++;
}
/*Last we return the res value multiplied by the sign value to return the
* number based on whether it was negative or not. NOTE: We have int in
* parenthesis to cast the rest * sign into a int so it can be returned as
* an int.*/
return ((int)(res * sign));
}