Ex_2.3_htoi.c

/**
 * Exercise 2.3 - htoi program, character to integer program.
 *
 */

#include<stdio.h>
#define MAXLINE 100

#define YES 1
#define NO 0

int mgetline(char line[], int maxline);
int htoi(char s[]);

int main(void)
{
	char line[MAXLINE];
	int value;

	mgetline(line, MAXLINE);
	value=htoi(line);

	printf("The value of %s is %d",line,value);

	return 0;
}

int mgetline(char s[],int lim)
{
	int c,i;

	for(i=0; i < lim-1 && (c=getchar()) != EOF && c!='\n'; ++i)
		s[i] =c;

	if(c=='\n')
	{
		s[i] =c;
		++i;
	}
	s[i] = '\0';

	return i;
}

int htoi(char s[])
{
	int hexdigit,i,inhex,n;
	i = 0;
	if( s[i] == '0')
	{
		++i;
		if(s[i] == 'x' || s[i] == 'X')
			++i;
	}

	n = 0;
	inhex = YES;

	for(;inhex==YES;++i)
	{
		if(s[i] >='0' && s[i] <='9')
			hexdigit= s[i] - '0';
		else if(s[i] >='a' && s[i] <='f')
			hexdigit= s[i] -'a' + 10;
		else if(s[i] >='A' && s[i] <='F')
			hexdigit= s[i] -'A' + 10;
		else
			inhex = NO;

		if(inhex == YES)
			n = 16 * n + hexdigit;
	}
	return n;
}