黑色星期五
有一种计算机病毒叫黑色星期五，如果当天是13号，又恰好是星期五，就会发作起来毁坏计算机的存储系统，试编程找出九十年代中这种病毒可能发作的日期。
1 #include <stdio.h> 2 #define DAYBEGIN 1990 3 #define DAYEND 1999 4 #define FRIDAY 5 5 6 static day_table[2][13] = { 7 0, 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31, 8 0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31, 9 }; 10 11 int main() 12 { 13 int day, month, year; 14 int weekday; 15 16 weekday = 1; //1990 1 1 is January 17 printf("The black friday is : \n"); 18 printf("year month day\n"); 19 for (year = DAYBEGIN; year <= DAYEND; ++year) { 20 if (year % 4 == 0 && year % 100 != 0 || year % 400 == 0) { 21 for (month = 1; month <= 12; month++) { 22 for (day = 1; day <= day_table[0][month]; day++, weekday++) { 23 if (day == 13 && weekday == FRIDAY) //find the black friday 24 printf("%d %2d %d\n", year, month, day); 25 if (weekday == 7) // a week has gone 26 weekday = 0; 27 } 28 } 29 } 30 else { 31 for (month = 1; month <= 12; month++) { 32 for (day = 1; day <= day_table[1][month]; day++, weekday++) { 33 if (day == 13 && weekday == FRIDAY) //find the black friday 34 printf("%d %2d %d\n", year, month, day); 35 if (weekday == 7) //a week has gone 36 weekday = 0; 37 } 38 } 39 } 40 } 41 return 0; 42 }
测试结果如图：
