C++菜鳥有問題越來越總計報名

Question

int main(void) 
{ 

    StartUp(); //indicates beginning of code 

    double startmileage{ 0 };    //indicates starting mileage, initialized at the value of 0 
    double endmileage{ 0 };    //indicates ending mileage, initialized at the value of 0 
    double milesdriven{ 0 };    //indicates total miles driven, initialized at the value of 0 
    double gallonsused{ 0 };    //indicates total gallons used, initialized at the value of 0 
    double milespergallon{ 0 };   //indicates total miles per gallon, initialized at the value of 0 
    double totalgallonsused{ 0 }; 
    double totalmilesdriven{ 0 }; 


    while (true) 
    { 
     cout << "Enter the gallons used (-1 to end): ";     //prompts user to enter total number of gallons used for trip 
     cin >> gallonsused;             //user enters data 
     totalgallonsused += gallonsused; 
     if (gallonsused == -1) 

     { 
      break;               // Check for sentinel value of -1 
     } 

     cout << "Enter starting mileage: ";        //prompts user to enter start mileage for trip 
     cin >> startmileage;            //user enters data 

     cout << "Enter ending mileage: ";         //prompts user to enter end mileage for trip 
     cin >> endmileage;             //user enters data 

     milesdriven = endmileage - startmileage;       //calculates total miles driven 
     totalmilesdriven += milesdriven; 

     cout << "Miles driven: " << milesdriven << endl;     //outputs total miles driven to screen 

     milespergallon = milesdriven/gallonsused;       //calculates total miles per gallon 

     cout << "The miles/gallon for this tank was: " << milespergallon << endl;   //outputs miles per gallon to screen 

     cout << "\n\n" << endl; 
    } 

    // Show grand totals 
    cout << "\n\nGrand totals: " << endl; 

    cout << "Total gallons used: " << totalgallonsused << endl; 
    cout << "Total miles driven: " << totalmilesdriven << endl; 
    cout << "The overall average verage miles/gallon: " << milespergallon <<endl; 

    cout << "\n\n" << endl; 



WrapUp(); 

這裏是輸出：

Enter the gallons used (-1 to end): 12.8 
Enter starting mileage: 0 
Enter ending mileage: 287 
Miles driven: 287 
The miles/gallon for this tank was: 22.4219 



Enter the gallons used (-1 to end): 10.3 
Enter starting mileage: 287 
Enter ending mileage: 487 
Miles driven: 200 
The miles/gallon for this tank was: 19.4175 



Enter the gallons used (-1 to end): 5 
Enter starting mileage: 487 
Enter ending mileage: 607 
Miles driven: 120 
The miles/gallon for this tank was: 24 



Enter the gallons used (-1 to end): -1 


Grand totals: 
Total gallons used: 27.1 
Total miles driven: 607 
The overall average verage miles/gallon: 24 



Program Program2.cpp ended successfully. 
Press any key to continue . . . 

Answer 1

你周圍循環，每次更換milesdriven。相反，你應該積累它：

milesdriven += endmileage - startmileage; 

你不需要計算每加侖的里程，直到循環之後。但是，你需要計算totalgallonsused：

totalgallonsused += gallonsused; 

而且在循環之後則：

milespergallon = milesdriven/totalgallonsused;