《C程序设计语言》第二版练习2-3参考程序

最近学C，在做C圣经的练习题，记录一下大神的成长史，哈哈哈，加油鸭

// 编写函数htoi(s), 把由十六进制数字组成的字符串（包含可选的前缀0X和0x），转化为与之等价的整数值, 字符串中包含的字符可以是0 - 9，A - F，a - f
#include <stdio.h>
#include <stdlib.h>
#define LINE 1000
#define TEN 10
#define SIX 16
int getline(char s1[], int n);
int htoi(char s2[]);
int main(void)
{
	char a1[LINE];
	int len;
	int m=0;
	while (len = getline(a1, LINE) > 0)
	{
		printf("The hex is ：%s\n", a1);
		m = htoi(a1);
		printf("The dec is ：%d\n", m);
	}
	system("pasue");
	return 0;
}
int getline(char s1[], int n)
{
	int i, c;
	for (i = 0; i < n - 1 && (c = getchar()) != EOF && c != '\n'; i++)
		s1[i] = c;
	s1[i] = '\0';
	return i;
}
int htoi(char s2[])
{
	int i = 0;
	int j = 1;
	int n = 0;
	while (s2[i] != '\0')
	{
		i++;
	}
	i--;
	while (s2[i] != 'X' && s2[i] != 'x' && i>=0)
	{
		if (s2[i] >= '0' && s2[i] <='9')
		{
			n = n + int(s2[i]-'0') * j;
			i--;
			j = j*SIX;
		}
		else if (s2[i] >= 'a' && s2[i] <= 'f')
		{
			n = n + (s2[i] - 'a' + TEN)*j;
			i--;
			j = j*SIX;
		}
		else  //(s2[i] >= 'A' && s2[i] <= 'F')
		{
			n = n + (s2[i] - 'A' + TEN)*j;
			i--;
			j = j*SIX;
		}
	}
	//printf("The dec is ：%d\n", n);
	return n;
}