C++ 输出错误

Question

感谢你们，这个程序的输出是固定的。除了学号。我读到评论说我从未为其设定值(value)，这让我感到困惑。

void process_file(ifstream& input)
    {
     int thisStudent = 0;

     StudentRecord student = StudentRecord(); 
        while (thisStudent++ < CLASS_SIZE)
        {
         student.input(input, thisStudent);
            student.computeGrade();
                student.output();
            }
        }

这不会将 studentNumber 设置为 0，然后在每次循环运行时加 +1。

 // Author: 
// Assignment 8
#include <iostream>
#include <fstream> 
#include <iomanip>
using namespace std;

ofstream     outputfile("output.txt");     

const int    MAX_FILE_NAME = 35;            
const int    CLASS_SIZE = 5;

class StudentRecord  
{
public:
void input( ifstream& input,int studentid);

void computeGrade();

void output();

private:
  int studentNumber;
  double exam1;
  double exam2;
  double exam3;
  double exam4;
  double average;
  char grade;
};


void open_input(ifstream& input, char name[]); 
void process_file(ifstream& input);            

int main() 
{  char again;             
   char file_name[MAX_FILE_NAME + 1];
   ifstream input_numbers;            

   cout << "This program can calculate the exam average and grade for\n"
        << "each student.\n" << endl;
   system("pause"); 

   do 
   {  
      system("cls");                          
      open_input(input_numbers, file_name);   
      process_file(input_numbers);             
      input_numbers.close();                   

      cout << "\nDo you want to process another file (Y/N)? ";
      cin >> again;
      cin.ignore(256, '\n');  

   } while ( again == 'y' || again == 'Y'); 

   cout << "\nEnd of Program!" << endl;
   outputfile << "\n\nThanks for using GradeCalc!\f"; 
   outputfile.close();

   return 0; 
}  

void process_file(ifstream& input)
{
 int thisStudent = 0;

 StudentRecord student = StudentRecord(); 
    while (thisStudent++ < CLASS_SIZE)
    {
     student.input(input, thisStudent);
        student.computeGrade();
        student.output();
    }
}

void open_input(ifstream& input, char name[]) 
{  int count = 0;             
   do 
   {  count++;
      if (count != 1)  
      {  cout << "\n\aInvalid file name or file does not exist. Please try again." 
              << endl;
      }
      cout << "\nEnter the input file name (maximum of " << MAX_FILE_NAME
           << " characters please)\n:> ";
      cin.get(name, MAX_FILE_NAME + 1);
      cin.ignore(256, '\n');           
      input.clear();                  
      input.open(name,ios_base::in); 
    } while (input.fail() );          
} 

void StudentRecord::input(ifstream& input, int studentid)
{
      input >> exam1 >> exam2 >> exam3 >> exam4;

}

void StudentRecord::computeGrade()
{
    average = (exam1 + exam2 + exam3 + exam4) / 4 ;
      if (average >= 90)
        grade = 'A'; 
else if (average >=  80)
  grade = 'B';
else if (average >= 70)
  grade = 'C';
else if (average >= 60)
  grade = 'D';
else if (average < 60)
  grade = 'F';
}

void StudentRecord::output()
{  
   cout << "\n\nThe record for student number:" << setw(8) << studentNumber << endl;
   cout << "The exam grades are:" << setw(8) << exam1 << exam2 << exam3 << exam4 << endl;
   cout << "The numeric average is:" << setw(8) << average << endl;
   cout << "and the letter grade assigned is:" << setw(8) << grade << endl;
}

Answer 1

好吧，studentNumber 是垃圾，因为您从来没有给它赋值。所以它只是在那个位置发生了任何已经在内存中的事情。

考试成绩打印错误，因为 C++ 中的逗号与您认为的不一样，这也是为什么添加 endl; 会给您带来错误的原因。

我将让您自己解决格式问题。您应该考虑阅读输出或至少进行一些试验和错误。