void add ( const char a[], const char b[], char res[]);
{
int digita = strlen(a);
int digitb = strlen(b);
int suma = 0;
int sumb = 0;

for(int i = 0; i < digita; i ++)
{
    suma *= 10;
    suma += (a[i] - '0');

}
for(int x = 0; x < digitb; x ++)
{
    sumb *= 10;
    sumb += (b[x] - '0');

}

int sum = suma + sumb;
char res[20];
sprintf(res, "%d\n", sum);
printf("%s\n", res);
}

void sub ( const char a[], const char b[], char res[]);
{
int digita = strlen(a);
int digitb = strlen(b);
int suma = 0;
int sumb = 0;

for(int i = 0; i < digita; i ++)
{
    suma *= 10;
    suma += (a[i] - '0');

}
for(int x = 0; x < digitb; x ++)
{
    sumb *= 10;
    sumb += (b[x] - '0');

}


int diff = suma - sumb;
char res2[20];
sprintf(res2, "%d\n", diff);
printf("%s\n", res2);


}