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Conversion Binary <-> Decimal

Posted on 2002-04-12
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Last Modified: 2013-11-15
Hi
I need two simple functions:

1 - Convert Binary to Decimal and returns this value
2-  Convert Decimal to Binary and returns this value

Thanks
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Question by:maomorta
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by:jonnin
Comment Utility
dec to bin:
what I do is make a hex lookup table

0 = "0000"
1 = "0001"
...
f = "1111"

and do an sprintf into a hex string.
int i, char * str...
sprintf(str, "%x", i);

then each hex digit is replaced with the
lookup value. Kill leading zeros if you want too...

bin to dec is easier
place the bits into an unsigned int  using shift operator
<< ...


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jonnin earned 100 total points
Comment Utility
come to think of it, you can shift the bits out instead of the sprintf thing...
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Expert Comment

by:Triskelion
Comment Utility
// Binary to Decimal
http://www.c-for-dummies.com/lessons/bonus/13/

// Decimal to Binary
http://mathforum.com/dr.math/problems/kaufman.10.26.99.html

I will try to make an example.
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Expert Comment

by:Triskelion
Comment Utility
// Cheap example.  Microsoft compiler
#include <stdio.h>
#include <stdlib.h>
#include <string.h>


long     BinaryToDecimal(const char * pstrBinary)
{
     int     intLoop=0;
     long     lngReturn=0L;
     long     lngMultip=1L;
     for (intLoop=0; intLoop < (int)strlen(pstrBinary); intLoop++)
          {
          if ('1' == pstrBinary[intLoop])
               {
               lngReturn += lngMultip;
               }
          lngMultip *= 2;
          }
     return     lngReturn;
}


char     *     DecimalToBinary(long lngDecimal)
{
     static     char strReturn[128]={0};
     _ltoa(lngDecimal, strReturn, 2);
     return strReturn;
}


int main(void)
{
     long          lngDecimal     =     7;
     char     *     pstrBinary     =     "111";


     printf("B2D=%ld\nD2B=%s\n",     BinaryToDecimal(pstrBinary),     DecimalToBinary(lngDecimal));
}
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Author Comment

by:maomorta
Comment Utility
Hi jonnin,
As you sugested I wrote this program but I have a segmentation fault, and I can not understand where the problem is.

Can you give more details about
"bin to dec is easier
place the bits into an unsigned int  using shift operator
<< ..."

#include <stdio.h>
#include <string.h>

void int2bin(long num);

int main()
{    
     int2bin(12343);    
}


void int2bin(long num)
{
     char *hex;
     char bin[50]="";
     sprintf(hex, "%X", num);              
     while (*hex) {
          switch (*hex)
            {
                     case '0':
                             strcat(bin, "0000");                
                break;          
              case '1':
                   strcat(bin, "0001");                
                break;          
              case '2':
                   strcat(bin, "0010");
                break;
              case '3':
                   strcat(bin, "0011");
                break;
              case '4':
                   strcat(bin, "0100");
                break;
              case '5':
                   strcat(bin, "0101");
                break;
              case '6':
                   strcat(bin, "0110");
                break;
              case '7':
                   strcat(bin, "0111");
                break;
              case '8':
                   strcat(bin, "1000");
                break;
              case '9':
                   strcat(bin, "1001");
                break;
              case 'A':
                   strcat(bin, "1010");
                break;
              case 'B':
                   strcat(bin, "1011");
                break;
              case 'C':
                   strcat(bin, "1100");
                break;
              case 'D':
                   strcat(bin, "1101");
                break;
              case 'E':
                   strcat(bin, "1110");
                break;
              case 'F':
                   strcat(bin, "1111");
                break;                                
          }
                                                 
          *hex++;
     }
     
     printf("%s\n", bin);          
                         
}
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Expert Comment

by:Shivshankar
Comment Utility
Make these changes...

char * hex; ----> to  
    char * hex = (char *)(malloc(sizeof(long)*2*sizeof(char)));
Also, add this as a better programming practice.
    char *start_addr = hex;

*hex++;   -----> to
   hex++; //Just hex++

At the end of the code:
  free(start_addr);
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Expert Comment

by:deighton
Comment Utility
char *int2bin(long lno,char *buf)
{
     int c = 32;
     


     buf[32]=0;
     do
     {
         
          buf[--c] = '0' + (lno & 1);
          lno = lno >> 1;
     }
     while (c);
     

     return buf;

}    


long bin2int(char *buf)
{
     long val=0;
     int c=0;


     while (buf[c])
     {
          val = (val << 1) | (buf[c++]-'0');
     }
         
     return val;

}


'example

printf("\n%s",int2bin(1024,test));
printf("\n%li",bin2int(test));

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