next_day.cpp

#include <stdio.h>
int main()
{
    int day, month, max_day;
 
    do {
        printf("Nhap ngay, thang: ");
        scanf("%d%d", &day, &month);
 
        if (month < 0 || month > 12) {
            printf("Nhap thang khong hop le (1-12)!\n");
            continue;
        }
 
        switch (month) {
            case 1: case 3: case 5: case 7: case 8: case 10: case 12:
                max_day = 31;
                break;
            case 2: max_day = 28; break;
            default: max_day = 30;
        }
 
        if (day < 0 || day > max_day) {
            printf("Ngay khong hop le (1-31)!\n");
            continue;
        }
        if (day >= max_day) {
            day = 1;
            month++;
 
            if (month > 12) month = 1;
        } else {
            day++;
        }
 
        printf("Ngay tiep theo: %d/%d", day, month);
        break;
    } while (1);
 
    return 0;
}