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From: rjohnson@shell.com (Roy Johnson)
Newsgroups: comp.lang.c
Subject: Re: Converting between bases
Message-ID: <RJOHNSON.91Mar6100915@olorin.shell.com>
Date: 6 Mar 91 16:09:15 GMT
References: <62375@eerie.acsu.Buffalo.EDU>
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Organization: Shell Development Company, Bellaire Research Center, Houston, TX
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In-Reply-To: cloos@acsu.buffalo.edu's message of 28 Feb 91 12:29:42 GMT

In article <62375@eerie.acsu.Buffalo.EDU> cloos@acsu.buffalo.edu (James H. Cloos) writes:
>Hello.

>I need to be able to convert arbitrarily long strings which a guaenteed to
>match one of the regexps below (each one gets a different function) and
>output the hex equivilent (again in a string) optionally cut down to a
>specified number of hex digits.  (The least significant ones.)  The latter
>part I can take care of, but the former is giving me trouble.

>[01]+
>[0-7]+
>[0-9]+

>If someone could give me a jab into the right direction (either what to do
>or where to look) I'd be most grateful.  

The following will work if the strings are not so arbitrarily long that
the machine cannot numerically represent them:

char hexstr[9];		/* The final result string */
char numstring[33];	/* The input string */
unsigned i;		/* Just a loop variable */
long num;		/* Numerical value of numstring */

Binary:
for(i=num=0; numstring[i] != '\0'; ++i) {
  num *= 2;
  if (numstring[i] == '1') ++num;
}
sprintf(hexstr, "%x", num);

Octal:
sscanf(numstring, "%o", &num);
sprintf(hexstr, "%x", num);

Decimal:
sscanf(numstring, "%d", &num);
sprintf(hexstr, "%x", num);

This looks suspiciously like homework, so I've purposely used
library routines, which most professors don't want you to use,
but which are fine more most real work.

--
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Roy Johnson, Shell Development Company