sum (adding 2 numbers ) without plus operator

Question

Can anyone explain the logic how to add a and b?

#include 

int main()
{
     int a=30000, b=20, sum;
     char *p;
             


        

Answer 1

/*
by sch.

001010101 = 85
001000111 = 71
---------
010011100 = 156
*/

#include 

#define SET_N_BIT(i,sum) ((1 << (i)) | (sum))

int sum(int a, int b)
{
    int t = 0;
    int i = 0;
    int ia = 0, ib = 0;
    int sum = 0;
    int mask = 0;

    for(i = 0; i < sizeof(int) * 8; i++)
    {   
        mask = 1 << i;
        ia = a & mask;
        ib = b & mask;

        if(ia & ib)
            if(t)
            {
                sum = SET_N_BIT(i,sum);
                t = 1;
                /*i(1) t=1*/
            }
            else
            {
                t = 1;
                /*i(0) t=1*/
            }
        else if (ia | ib)
            if(t)
            {
                t = 1;
                /*i(0) t=1*/
            }
            else
            {
                sum = SET_N_BIT(i,sum);
                t = 0;
                /*i(1) t=0*/
            }
        else
            if(t)
            {
                sum = SET_N_BIT(i,sum);
                t = 0;
                /*i(1) t=0*/
            }
            else
            {
                t = 0;
                /*i(0) t=0*/
            }

    }

    return sum;
}

int main()
{
    int a = 85;
    int b = 71;
    int i = 0;

    while(1)
    {
        scanf("%d %d", &a, &b);

        printf("%d: %d + %d = %d\n", ++i, a, b, sum(a, b));
    }

    return 0;
}