Question

请放轻松我，因为我是C ++的新手，目前正在编程介绍课程:)

我目前在获取正确编译的do \ while语句时遇到问题。我的目标是输入以下内容，直到输入-1的标记值，这将结束该过程并给出我的值的累计总数。

以下是我需要为每个实体输入的值：

import requests

table_data = requests.get('http://bonusbagging.co.uk/odds-server/getdata_slow.php').content

输入标记值后，应计算所有实体组合的以下内容：

 gallons used 
 starting mileage
 ending mileage
 miles driven
 miles per gallon

以下是我到目前为止的情况，但输入-1时并没有结束。当输入-1时，我还没有添加最终值，因为我不确定如何继续并且我试图让第1部分首先正常工作。以下是我的代码（请原谅评论）：

total gallons used
total miles driven
overall average miles per gallon

以下是发生的事情：

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
    long double milespergallon{ 0 };       //indicates total miles per gallon, initialized at the value of 0

    do
    {
        cout << "enter the gallons used:  ";                                //prompts user to enter total number of gallons used for trip
        cin >> gallonsused;                                                 //user enters data

        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 = startmileage + endmileage;                            //calculates total miles driven

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

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

        cout << "Miles Per Gallon:  " << milespergallon << endl;            //outputs miles per gallon to screen
    } 

    while (gallonsused != -1);
WrapUp();  //indicates end of code

    return Success;

}

如您所见，它循环，但在输入标记值时不会停止

非常感谢任何帮助！

谢谢！

Answer 1

在用户响应所有其他提示并计算里程后，您不会在循环结束前测试gallonsused != -1。

不是使用do-while()，而是在用户输入后立即测试gallonsused，然后退出循环。

您还需要驱动总里程数和使用的总加仑数的变量。在每次输入之后，您将该行程的值添加到总计中，并在最后的总计中使用它们。

double totalmiles = 0;
double totalgallons = 0;

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

        totalgallons += gallonsused;

        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 = startmileage + endmileage;                            //calculates total miles driven

        totalmiles += milesdriven;

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

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

        cout << "Miles Per Gallon:  " << milespergallon << endl;            //outputs miles per gallon to screen
    } 

   // Show grand totals
    cout << "Grand totals:" << endl;

    cout << "Total Miles Driven: " << totalmiles << endl;
    cout << "Total Miles Per Gallon: " << totalmiles/totalgallons << endl;

    WrapUp();

Answer 2

循环体（花括号之间）被视为一个单元，由do-while控件重复。在cin用于检查-1的加仑后尝试放置if语句，使用break来退出循环。尝试这一点应该会有所帮助。

Answer 3

/dev/null表达式，就像while循环中的条件一样，在代码中的位置进行评估，它们不是监督。

for

输出：

#include <iostream>

int main() {
   int i = 0;
   do {
       std::cout << i << " ";
       i += 2;
       std::cout << i << ' ';
       i -= 1;
       std::cout << i << ' ';
   } while (i != 2);
}

现场演示：http://ideone.com/7JWLp7

do \ while语句无法正确编译（初学者）

3 个答案: