spoj question http://www.spoj.com/problems/JULKA/

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

       #define MAX 111

       char klaudia[MAX], natalia[MAX], total[MAX], diff[MAX];

      void calc()
     {
         int len1 = strlen(total);
         int len2 = strlen(diff);
int a, b, c, i, j, k, f;
char temp[MAX];

for(i=len1-1, j=len2-1, k=c=0; i>=0 || j>=0 || c; i--, j--, k++)
{
    a = i>=0? total[i]-'0' : 0;
    b = j>=0? diff[j]-'0' : 0;
    temp[k] = (a+b+c)%10 + '0';
    c = (a+b+c)/10;
}
temp[k] = 0;

strcpy(klaudia,"0");
//expalin the for loop what is actually being done here//
for(i=k-1, j=a=f=0; i>=0; i--)
{
    b = (a*10 + temp[i]-'0') / 2;
    a = (a*10 + temp[i]-'0') % 2;
    if(b) f = 1;
    if(f) klaudia[j++] = b+'0';
}
if(!j) j++;
klaudia[j] = 0;

for(i=len1-1, j=len2-1, k=c=0; i>=0; i--, j--, k++)
{
    a = total[i]-'0';
    b = j>=0? diff[j]-'0' : 0;
    if(a < b+c)
    {
        temp[k] = (10+a-b-c) + '0';
        c = 1;
    }
    else
    {
        temp[k] = a-b-c + '0';
        c = 0;
    }
}
temp[k] = 0;

    strcpy(natalia,"0");
    for(i=k-1, j=a=f=0; i>=0; i--)
    {
            b = (a*10 + temp[i]-'0') / 2;
            a = (a*10 + temp[i]-'0') % 2;
            if(b) f = 1;
            if(f) natalia[j++] = b+'0';
    }
    if(!j) j++;
    natalia[j] = 0;

}

   int main()
 {
        while(scanf("%s %s", total, diff)==2)
         {
            calc();
            printf("%s\n%s\n", klaudia, natalia);
        }

     return 0;

}
expalin the for loop what is actually being done there

//