#include <stdio.h>

int main(void) {
	int teste1 = carries(9, 1);
	int teste2 = carries(99, 1);
	int teste3 = carries(999, 1);
	int teste4 = carries(999, 10);
	
	printf("9+1: %i carries\n", teste1);
	printf("99+1: %i carries\n", teste2);
	printf("999+1: %i carries\n", teste3);
	printf("999+10: %i carries\n", teste4);
	
	return 0;
}

int carries(int a, int b) {
	return (sumDigits(a) + sumDigits(b) - sumDigits(a+b)) / 9;
}

int sumDigits(int num) {
	int sum = 0;
    while (num != 0) {
        sum += num % 10;
        num /= 10;
    }
    return sum;
}