Yes, it's yet another thread about implementing three basic operations (addition, subtraction and multiplication) on abnormally large numbers (> 100 digits).

I've stored each digit inside an array of `int`

s, as the following piece of code illustrates

```
while((ch = getchar()) != EOL)
a[len_a++] = ch - CHR;
```

Now, when it comes to adding them, I add the *(len_number - k)*th digits of both numbers, compute their reminder and their quotient, and store the reminder on the *k*th place of the `sum`

array. The following piece of code works nicely for, say, 132 and 32, but when I try adding 1248 and 2, the result 1950, instead of 1350. I think I'm doing some illegal work on the arrays (at some point, I have something like `b[1 - 3]`

), but I've been struggling for a lot of time and I still can't figure things out, so any help would be highly appreciated.

```
for(i = 1; i <= len_a || i <= len_b; ++i) {
aux = (a[len_a - i] + b[len_b - i] + qtt);
rem = aux % 10;
sum[i - 1] = rem;
++len_sum;
qtt = aux / 10;
}
```

And here's the big picture

```
#include <stdio.h>
#define NR_DIG 100
#define EOL '\n'
#define CHR '0'
int main(void) {
unsigned short a[NR_DIG], b[NR_DIG], sum[NR_DIG + 1];
int ch, len_a = 0, len_b = 0, len_sum = 0, rem, qtt = 0, i, aux;
printf("a: ");
while((ch = getchar()) != EOL)
a[len_a++] = ch - CHR; /* ch - CHR = input - its character part */
printf("b: ");
while((ch = getchar()) != EOL)
b[len_b++] = ch - CHR;
for(i = 1; i <= len_a || i <= len_b; ++i) {
aux = (a[len_a - i] + b[len_b - i] + qtt);
rem = aux % 10;
sum[i - 1] = rem;
++len_sum;
qtt = aux / 10;
}
printf("a + b: ");
for(i = len_sum - 1; i >= 0; --i)
printf("%hu", sum[i]);
printf("\n");
return 0;
}
```