我的代码出错了，谁能解释一下怎么回事？

Question

我是 C++ 新手，我正在开发一个程序，但在第 39 行它显示错误“else”，没有先前的“if”，但我确实有一个先前的 if。有人对我做错了什么有任何意见吗？这是我的程序代码。谢谢。

1 #include <fstream>
2 #include <iostream>
3 #include <cstdlib>
4 using namespace std;
5 int main()
6 { 
7 //Declarations
8     ifstream masterFile;
9     ifstream transactionFile;
10    ofstream newMasterFile;
11    double mClientNumber, mtotalClientCost, tClientNumber, titemClientCost;
12    string mClientfName, mClientlName;
13 cout << "Master File Updating Starting" ;
14 masterFile.open("Master.rtf");
15 transactionFile.open("Transaction.rtf");
16 newMasterFile.open("newMaster.rtf");
17 masterFile >> mClientNumber;
18 masterFile >> mClientfName;
19 masterFile >> mClientlName;
20 masterFile >> mtotalClientCost;
21 transactionFile >> tClientNumber;
22 transactionFile >>titemClientCost;
23 while ( transactionFile.eof() )
24 {
25     while (( masterFile.eof()) && (mClientNumber < tClientNumber))
26     {
27         newMasterFile << mClientNumber << endl;
28         newMasterFile << mClientfName << endl;
29         newMasterFile << mClientlName << endl;
30         newMasterFile << mtotalClientCost << endl;
31         masterFile >> mClientNumber;
32         masterFile >> mClientfName;
33         masterFile >> mClientlName;
34         masterFile >> mtotalClientCost;
35     }
36     if (masterFile.eof());
37    {
38         cout << "Error Client ID: " << tClientNumber << " not in Master File." ;
39     else if (mClientNumber == tClientNumber);
40         mtotalClientCost = mtotalClientCost + titemClientCost;
41         newMasterFile << mClientNumber << endl;
42         newMasterFile << mClientfName << endl;
43         newMasterFile << mClientlName << endl;
44         newMasterFile << mtotalClientCost << endl;
45         masterFile >> mClientNumber;
46         masterFile >> mClientfName;
47         masterFile >> mClientlName;
48         masterFile >> mtotalClientCost;
49     else if (mClientNumber > tClientNumber);
50         cout << "Error Client ID: " << tClientNumber << " not in Master File." ;
51     }
52     transactionFile >> tClientNumber;
53     transactionFile >> titemClientCost;
54 }
55 while (masterFile.eof())
56 {
57         newMasterFile << mClientNumber << endl;
58         newMasterFile << mClientfName << endl;
59         newMasterFile << mClientlName << endl;
60         newMasterFile << mtotalClientCost << endl;
61         masterFile >> mClientNumber;
62         masterFile >> mClientfName;
63         masterFile >> mClientlName;
64         masterFile >> mtotalClientCost;
65 }
66 cout << "Master File Updating Complete" ;
67
68 masterFile.close();
69 transactionFile.close();
70 newMasterFile.close();
71
72   system("pause");
73   return 0;
74 }

Answer 1

if (masterFile.eof());
                  //^^this ; here effectively terminates your if block and 
                 //does not have a closing } before else

类似的问题可以在这里找到：

if (mClientNumber == tClientNumber);
                                //^^another line below same problem

Answer 2

在所有 if 语句中，您添加了一个不必要的 ;。

if (masterFile.eof());{
//                   ^ this semicolon is not supposed to be there

; 将终止 if 语句。

改为这样做：

if (masterFile.eof()){

此外，您没有关闭 if 语句中的第一个括号。所以最终的产品应该是这样的：

if (masterFile.eof()){
    //if body
}else if (*next condition*){
    //else if body
}

等等..干杯

Answer 3

首先你在 if 和 else if 语句之后放置了一个分号

if (masterFile.eof());

else if (mClientNumber == tClientNumber);

替换它们。

如果不考虑这个错字 yjen，else if 没有前面的 if 语句。相反，它被放入封闭 if 语句的复合语句中

if (masterFile.eof());
{
     cout << "Error Client ID: " << tClientNumber << " not in Master File." ;
     else if (mClientNumber == tClientNumber);

也许你的意思是以下

if (masterFile.eof());
{
     cout << "Error Client ID: " << tClientNumber << " not in Master File." ;
}
else if (mClientNumber == tClientNumber);

或者

if (masterFile.eof());
{
     cout << "Error Client ID: " << tClientNumber << " not in Master File." ;
     if (mClientNumber == tClientNumber);

Answer 4

您在少数地方忘记了{ 和}。将第 36-51 行更改为

36    if (masterFile.eof())
37    {
38         cout << "Error Client ID: " << tClientNumber << " not in Master File." ;
39    } else if (mClientNumber == tClientNumber){
40         mtotalClientCost = mtotalClientCost + titemClientCost;
41         newMasterFile << mClientNumber << endl;
42         newMasterFile << mClientfName << endl;
43         newMasterFile << mClientlName << endl;
44         newMasterFile << mtotalClientCost << endl;
45         masterFile >> mClientNumber;
46         masterFile >> mClientfName;
47         masterFile >> mClientlName;
48         masterFile >> mtotalClientCost;
49     } else if (mClientNumber > tClientNumber){
50         cout << "Error Client ID: " << tClientNumber << " not in Master File." ;
51     }