Converting hex to dec problems

This is a discussion on Converting hex to dec problems within the C Programming forums, part of the General Programming Boards category; For some reason my algorithm to convert a hexadecimal number into a decimal number doens't work and I cna't figure ...

  1. #1
    Slime Dragoon_42's Avatar
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    Converting hex to dec problems

    For some reason my algorithm to convert a hexadecimal number into a decimal number doens't work and I cna't figure it out. Any help would be appreciated.
    Code:
    #include<string.h>
    #include<math.h>
    #include<stdio.h>
    
    //dest is a character array that holds my hexedecimal string
    int todecimal(char *dest)
    {
    	int pos, sum, power_of_16;
                    //pos is the current element in the dest array
    	
    	pos=strlen(dest);
    	power_of_16=0;
    	
    	sum=0;
    	do{
    		--pos;
    		if(dest[pos]<=9)
    			sum+=dest[pos]*pow(16,power_of_16);
    		switch(dest[pos]){
    			case 'a': sum+=10*pow(16,power_of_16);
    				break;
    			case 'b':sum+=11*pow(16,power_of_16);
    			        break;
    			case 'c':sum+=12*pow(16,power_of_16);
    				break;
    			case 'd':sum+=13*pow(16,power_of_16);
    				break;
    			case 'e':sum+=14*pow(16,power_of_16);
    				break;
    			case 'f':sum+=15*pow(16,power_of_16);
    				break;
    			default: /*do nothing*/
    				break;
    		}
    		power_of_16++;
    	}while(pos!=0);
    	
    	return sum;
    }

  2. #2
    Just Lurking Dave_Sinkula's Avatar
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    >if(dest[pos]<=9)

    The character value of a text digit may not be a decimal value. For example, an ASCII '4' is equal to 0x34, which is equal to 52. You may want to use the following.
    Code:
    if ( dest[pos]-'0'<=9 )
       sum+=(dest[pos]-'0')*pow(16,power_of_16);
    7. It is easier to write an incorrect program than understand a correct one.
    40. There are two ways to write error-free programs; only the third one works.*

  3. #3
    Slime Dragoon_42's Avatar
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    May I ask what that does exactly? I'm new to C, but have been using C++ for a couple of years. Let me guess, it subtracts the ASCII value of zero from the ASCII value of dest[pos] and that should fix it?
    Last edited by Dragoon_42; 10-16-2003 at 07:03 PM.

  4. #4
    Just Lurking Dave_Sinkula's Avatar
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    Code:
    #include<stdio.h>
    
    int main(void)
    {
       int i;
       for(i = '0'; i <= '9'; ++i)
       {
          printf("i = '%c' = %d, i - '0' = %d - %d = %d\n", i, i, i, '0', i - '0');
       }
       return 0;
    }
    
    /* my output
    i = '0' = 48, i - '0' = 48 - 48 = 0
    i = '1' = 49, i - '0' = 49 - 48 = 1
    i = '2' = 50, i - '0' = 50 - 48 = 2
    i = '3' = 51, i - '0' = 51 - 48 = 3
    i = '4' = 52, i - '0' = 52 - 48 = 4
    i = '5' = 53, i - '0' = 53 - 48 = 5
    i = '6' = 54, i - '0' = 54 - 48 = 6
    i = '7' = 55, i - '0' = 55 - 48 = 7
    i = '8' = 56, i - '0' = 56 - 48 = 8
    i = '9' = 57, i - '0' = 57 - 48 = 9
    */
    7. It is easier to write an incorrect program than understand a correct one.
    40. There are two ways to write error-free programs; only the third one works.*

  5. #5
    Slime Dragoon_42's Avatar
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    Thank you very much! Now I'll move on to trying to convert signed decimals to 2's complement binary. I really appreciate the help!

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