十六进制转成十进制

#include <stdio.h>
#include <stdlib.h>
/* Here's a helper function to get me around the problem of not
* having strchr
*/
int hexalpha_to_int(int c) //把 aAbBcCdDeEfF 转成 10->15;

{
	char hexalpha[] = "aAbBcCdDeEfF";
	int i;
	int answer = 0;
	for(i = 0; answer == 0 && hexalpha[i] != '\0'; i++)
	{
		if(hexalpha[i] == c)
		{
			answer = 10 + (i / 2);
		}
	}
	return answer;
}
unsigned int htoi(const char s[])
{
	unsigned int answer = 0;
	int i = 0;
	int valid = 1;
	int hexit;
	if(s[i] == '0')
	{
		++i;
		if(s[i] == 'x' || s[i] == 'X')
		{
			++i;
		}
	}

	while(valid && s[i] != '\0')
	{
		answer = answer * 16;
		if(s[i] >= '0' && s[i] <= '9')
		{
			answer = answer + (s[i] - '0');
		}
		else
		{
			hexit = hexalpha_to_int(s[i]);
			if(hexit == 0)
			{
				valid = 0;
			}
			else
			{
				answer = answer + hexit;
			}
		}
		++i;
	}
	if(!valid)
	{
		answer = 0;
	}
	return answer;
}
/* Solution finished. This bit's just a test driver, so
* I've relaxed the rules on what's allowed.
*/
int main(void)
{
	char *endp = NULL;
	char *test[] =
	{
		"F00",
		"bar",
		"0100",
		"0x1",
		"0XA",
		"0X0C0BE",
		"abcdef",
		"123456",
		"0x123456",
		"deadbeef",
		"zog_c"
	};
	unsigned int result;
	unsigned int check;
	size_t numtests = sizeof test / sizeof test[0];


	size_t thistest;
	for(thistest = 0; thistest < numtests; thistest++)
	{
		result = htoi(test[thistest]);
		check = (unsigned int)strtoul(test[thistest], &endp, 16);
		if((*endp != '\0' && result == 0) || result == check)
		{
			printf("Testing %s. Correct. %u\n", test[thistest], result);
		}
		else
		{
			printf("Testing %s. Incorrect. %u\n", test[thistest], result);
		}
	}
	return 0;
}

结果如下：