c++ - 嵌套 If 困境

Question

我无法理解这个问题。该代码非常基本，但它的行为却出乎意料。该代码是例程的简化版本，用于从每日数据库中提取每月第 15 天的数据并将其保存到单独的文件中。哪里有问题 ？第一个 cout 打印输入外部 if 的任何一天的编号。然后是一些条件行来选择正确的日期(在这个例子中不是很重要)然后是 block ，内部 if，它应该将第 15 天的数据打印到新文件。现在，正如您所看到的，虽然外循环(注意!)仅在 10 日输入(这已经是错误的 - 它应该写入从 11 到 15 的所有数字)但随后它也打印出文件已写入15号!哪里有问题 ？ OUTER IF 10号才进，INNER IF怎么15号执行？？？？

#include "stdafx.h"
#include <iostream>
#include <string>

using namespace std;


int main()
{
    string newdata="mamma";
    string risultato="-";
    string PriorLine="-";
    int PriorDay=0;
    int lastmonth=0;

        // Loops through all the months
        for (int mese=1; mese <=12; mese++)
        { 
            //Loops through all the days in the month
            for(int day=1; day<=30; day++)
            {
                // at the month's beginning these 2 strings are set ="-"
                if (mese != lastmonth)
                {
                 risultato="-";
                 PriorLine="-";
                 }
                // if we are between the 10th and the 20th and the result is still to be found
                if (day>=10 && day<=20 && risultato=="-")
                {   
                       cout << day << endl;  // LISTS ALL THE DAYS THIS LOOP IS ENTERED
                       if (day=15)  // if it is exactly day 15 print that day's result
                              risultato=newdata;    
                       // if that month in the data there is no day 15 and 
                       // this is the second pass, choose the closest !  
                       if (day>15 && PriorLine !="-")
                       {
                            if (abs(day-15)<=abs(15-PriorDay))
                                   risultato=newdata;
                            else
                                   risultato=PriorLine;
                        }
                        PriorLine=newdata;
                        PriorDay=day;
                        if (risultato != "-")
                        {   
                            // writes the result ( risultato ) in a file
                            cout << "file written on the " << day << endl;

                         }
                 }                  
                 lastmonth=mese;
           }
    }    
    system("pause");
    return 0;

Answer 1

if (day=15) 将 15 分配给 day 并返回 true。你需要 if (day==15)