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Binary addition in C

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Join Date: Oct 2007

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Jammie

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Binary addition in C

May 28th, 2009

Hi there,

I tried binary addition. It seems to work fine. Could someone tell me if there's a better way of doin this or any bugs that could be uncovered in the code below?

I appreciate your time.

Thanks,
Tina

 Help with Code Tags 
 c Syntax (Toggle Plain Text) 
#include <stdio.h>
 
void binaryAdd(char *, char *);
 
int main()
{
	char op1[20], op2[20];
	char sum[20];
	char *p, *p1;
 
	fgets(op1, sizeof(op1), stdin);
	fgets(op2, sizeof(op2), stdin);
 
    if( (p = strchr(op1, '\n')) != NULL)
		*p = '\0';
 
    if( (p1 = strchr(op2, '\n')) != NULL)
	    *p1 = '\0';
 
	binaryAdd(op1, op2);
 
	return 0;
}
 
void binaryAdd(char *first, char *second)
{
	int carry = 0;
    int flen = strlen(first);
	int slen = strlen(second);
 
    char *tfirst = first + strlen(first) - 1;
	char *tsecond = second + strlen(second) - 1;
 
	int *result = malloc(sizeof(int) * 16);
    int *temp = result;
 
 
	for(; flen > 0 || slen > 0; flen--, slen--)
	{
        if((*tfirst - '0') ^ (*tsecond - '0'))
		{
			if(!carry)
			{
				*temp++ = 1 + carry;  
				carry = 0;
			}
			else
				*temp++ = 0;
		}
		else
		{
			if((*tfirst - '0') & (*tsecond -'0'))
			{
				*temp++ = (0 + carry);
				carry = 1;
			}
			else
			{
				*temp++ = (0 + carry);
				carry = 0;
			}
		}
 
		tfirst--;
		tsecond--;
	}
 
	if (carry == 1)
	{
		*temp++ = carry;
	}
 
    while(temp-- != result)
		printf("%d", *temp);
 
	free(result);
}
#include <stdio.h>

void binaryAdd(char *, char *);

int main()
{
	char op1[20], op2[20];
	char sum[20];
	char *p, *p1;

	fgets(op1, sizeof(op1), stdin);
	fgets(op2, sizeof(op2), stdin);

    if( (p = strchr(op1, '\n')) != NULL)
		*p = '\0';

    if( (p1 = strchr(op2, '\n')) != NULL)
	    *p1 = '\0';

	binaryAdd(op1, op2);

	return 0;
}

void binaryAdd(char *first, char *second)
{
	int carry = 0;
    int flen = strlen(first);
	int slen = strlen(second);

    char *tfirst = first + strlen(first) - 1;
	char *tsecond = second + strlen(second) - 1;

	int *result = malloc(sizeof(int) * 16);
    int *temp = result;


	for(; flen > 0 || slen > 0; flen--, slen--)
	{
        if((*tfirst - '0') ^ (*tsecond - '0'))
		{
			if(!carry)
			{
				*temp++ = 1 + carry;  
				carry = 0;
			}
			else
				*temp++ = 0;
		}
		else
		{
			if((*tfirst - '0') & (*tsecond -'0'))
			{
				*temp++ = (0 + carry);
				carry = 1;
			}
			else
			{
				*temp++ = (0 + carry);
				carry = 0;
			}
		}
	
		tfirst--;
		tsecond--;
	}

	if (carry == 1)
	{
		*temp++ = carry;
	}
	
    while(temp-- != result)
		printf("%d", *temp);

	free(result);
}

Last edited by Ancient Dragon; May 28th, 2009 at 11:49 pm. Reason: corrected code tags

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Join Date: Feb 2008

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jephthah

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Re: Binary addition in C

May 28th, 2009

why so complicated? all you really need is "strtol()" and the addition operator.

 Help with Code Tags 
 c Syntax (Toggle Plain Text) 
int binaryAdd(char *first, char *second, int *sum)
{
    int val1, val2;
    char *ptr1, *ptr2;
    size_t length;
 
    val1 = strtol(first,&ptr1,2);
    val2 = strtol(second,&ptr2,2);
 
    if (ptr1 == first || ptr2 == second)
    {
        printf("\ninvalid entry.\n\n");
        return 0;
    }
 
    length = ptr1-first;
    if ((ptr2-second) > length)
        length = ptr2-second;
 
    *sum = val1+val2;
 
    printf("\n  %*s (%d)\n+ %*s (%d)\n\n= %*s (%d)\n\n",
        length, first, val1, length, second, val2, length, " ", *sum);
 
    return 1;
}
int binaryAdd(char *first, char *second, int *sum)
{
    int val1, val2;
    char *ptr1, *ptr2;
    size_t length;

    val1 = strtol(first,&ptr1,2);
    val2 = strtol(second,&ptr2,2);

    if (ptr1 == first || ptr2 == second)
    {
        printf("\ninvalid entry.\n\n");
        return 0;
    }

    length = ptr1-first;
    if ((ptr2-second) > length)
        length = ptr2-second;

    *sum = val1+val2;

    printf("\n  %*s (%d)\n+ %*s (%d)\n\n= %*s (%d)\n\n",
        length, first, val1, length, second, val2, length, " ", *sum);

    return 1;
}

(The rest is just decoration)

I'll leave conversion of the numeric sum, back into a binary string, as an exercise to the reader

Last edited by jephthah; May 29th, 2009 at 12:00 am.

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Join Date: Oct 2007

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Jammie

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Re: Binary addition in C

May 29th, 2009

Hi,

Thanks for responding!

I was thinking of doing it at the bit level using the bit operators.

Thanks again,
Tina

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jephthah

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Re: Binary addition in C

May 29th, 2009

at the "bit level", every integer is inherently binary and hex and decimal... it does not matter, because there's only a difference when you print it.

so, you can make it hard if you like, just for the sake of having a challenge or if your instructor requires you to do so for learning purposes.

but if you're not required to make it difficult, i'd say use the <stdlib.h> standard library functions whenever possible.

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Join Date: Aug 2008

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monkey_king monkey_king is offline

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Junior Poster

Re: Binary addition in C

May 29th, 2009

Well, this isn't at the bitlevel,

you are interpreting the ascii values '0' '1' as bit 0 and bit 1.

If you are interested in this bitlevel stuff,
you should look into the shift operations. like

 Help with Code Tags 
 c++ Syntax (Toggle Plain Text) 
unsigned char x=7;
unsigned char y=x<<1;
//y is now 7 times 2
unsigned char x=7;
unsigned char y=x<<1;
//y is now 7 times 2

But it looks nice your code,
one thing though, you don't need

 Help with Code Tags 
 c++ Syntax (Toggle Plain Text) 
if (carry == 1)
    *temp++ = carry;
//just
if(carray)
if (carry == 1)
    *temp++ = carry;
//just
if(carray)

A good exercise is to write you addition program with a non fixed base like,

$<br /> digit_n = (digit_{n-1}\textrm{ div }base) + (digit_n\textrm{ mod }base)<br />$