Binary addition in C
 

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

#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);

}

Re: Binary addition in C
 

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

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 :P


.

Re: Binary addition in C
 

Hi,

Thanks for responding!

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

Thanks again,
Tina

Re: Binary addition in C
 

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.

Re: Binary addition in C
 

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

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

if (carry == 1)

    *temp++ = carry;

//just

if(carray)

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