include?"iostream" using?namespace?std; int?main() { ????int?year,?month,?day; ????int?days; ????int?sum; ????cout?<<?"請輸入年："; ????cin?>>?year; ????cout?<<?"請輸入月："; ????cin?>>?month; ????cout?<<?"請輸入日："; ????cin?>>?day; ????cout?<<?"請輸入日期"; ????cin?>>?days; ????switch(month) ????{? ????????case?1: ????????sum?=?0; ????????break; ????????case?2: ????????sum?=?31; ????????break; ????????case?3: ????????sum?=?59; ????????break; ????????case?4: ????????sum?=?90; ????????break; ????????case?5: ????????sum?=?120; ????????break; ????????case?6: ????????sum?=?151; ????????break; ????????case?7: ????????sum?=?181; ????????break; ????????case?8: ????????sum?=?212; ????????break; ????????case?9: ????????sum?=?243; ????????break; ????????case?10: ????????sum?=?273; ????????break; ????????case?11: ????????sum?=?304; ????????break; ????????case?12: ????????sum?=?334; ????????break; ????????default: ????????cout?<<?"你輸入的月份有誤。"; ????????break; ????} ????sum?+=?day?-?1; ????//減1的目的是為了保證當sum值為0時，year仍為當年 ????if?(year?%?400?==?0?||?(year?%?100?!=?0?&&?year?%?4?==?0)) ????????{ ????????????if?(month?>?2) ????????????sum++; ????????????//如果該年為閏年，且月份大于2月，那么sum值加1 ????????} ????days?-=?sum; ????//將天數減去sum的值 ????while?(days?>?365) ????//如果天數大于365 ????{ ????????if?((year?-?1)?%?400?==?0?||?(year?-?1)?%?100?!=?0?&&?(yea?r-?1)?%?4?==?0) ????????//如果該年減1后的年為閏年 ????????{ ????????????days?-=?366; ????????????//天數減366 ????????} ????????else ????????{ ????????????days?-=?365; ????????????//否則天數減365 ????????} ????????year?-=?1; ????????//年份隨之減1 ????} ????while?(365?>=?days?>?0) ????//當天數不大于365且大于0時 ????{ ????????days?-=?1; ????????day?-=?1; ????????//天數減1，日隨之減1 ????????if?(day?==?0) ????????//如果日為0 ????????{ ????????????if?(month?==?1) ????????????//如果月為1 ????????????{ ????????????????month?=?12; ????????????????day?=?31; ????????????????year?-=?1; ????????????????//月份更改為12，日更改為31，年減1 ????????????} ????????????else?if?(month?==?5?||?month?==?7?||?month?==?10?||?month?==?12) ????????????//如果月為5，7，10，12 ????????????{ ????????????????day?=?30; ????????????????month?-=?1; ????????????????//天數更改為30，月減1 ????????????} ????????????else?if?(?month?==?2?||?month?==?4?||?month?==?6?||?month?==?8?||?month?==?9?||?month?==?11) ????????????//如果月為2，4，6，8，9，11 ????????????{ ????????????????day?=?31; ????????????????month?-=?1; ????????????????//天數更改為31，月減1 ????????????} ????????????else?if?(month?==?3) ????????????//如果月為3 ????????????{ ????????????????if?(year?%?400?==?0?||?year?%?100?!=?0?&&?year?%?4?==?0) ????????????????//如果當年為閏年 ????????????????{ ????????????????????day?=?29; ????????????????????month?-=?1; ????????????????????//天數更改為29，月減1 ????????????????} ????????????????else ????????????????{ ????????????????????day?=?28; ????????????????????month?-=?1; ????????????????????//否則天數更改為28，月減1 ????????????????} ????????????} ????????????else ????????????//如果月不是以上的值 ????????????????cout?<<?"此月份不存在。"; ????????} ????} ????cout?<<?"計算得到的日期是"?<<?year?<<?"年"?<<?month?<<?"月"?<<?day?<<?"日"; ????return?0; }這段代碼的目的大致如下：輸入年、月、日后，輸入一個天數（大于0），計算該日期指定天數之前的日期。例如：依次輸入2032、9、25、1836，計算2032年9月25日的1836天之前的日期。具體過程，請參考注釋。但是在測試過程中，總是出現年為負數，月和日也不正確的結果。這是什么原因？