C - HtoI: Convert a string of hexadecimal digits into its equivalent integer value

淩亂°似流年 2022-10-26 15:29 172阅读 0赞

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/*
     * Write a function HtoI(s), which converts a string of hexadecimal digits
     * (including an optional 0x or 0X) into its equivalent integer value.
     * The allowable digits are 0 through 9, a through f, and A through F.
     *
     * HtoI.c - by FreeMan
     */
    
    #include <stdio.h>
    #include <ctype.h>
    
    unsigned long HtoI(const char s[]);
    
    int main()
    {
    	printf("%ld\n", HtoI("0xFA9C"));
    	printf("%ld\n", HtoI("0xFFFF"));
    	printf("%ld\n", HtoI("0X1111"));
    	printf("%ld\n", HtoI("0XBCDA"));
    
    	return 0;
    }
    
    unsigned long HtoI(const char s[])
    {
    	unsigned long n = 0;
    
    	for (int i = 0; s[i] != '\0'; i++)
    	{
    		int c = tolower(s[i]);
    		if (c == '0' && tolower(s[i + 1]) == 'x')
    		{
    			i++;
    		}
    		else if (c >= '0' && c <= '9')
    		{
    			n = 16 * n + (c - '0');
    		}
    		else if (c >= 'a' && c <= 'f')
    		{
    			n = 16 * n + (c - 'a' + 10);
    		}
    	}
    
    	return n;
    }
    
    // Output:
    /*
    64156
    65535
    4369
    48346
    
    */

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