C++ C+的新功能+；，编码语法

我在空闲时间编写的代码可以使用帮助。我是C++初学者。我正在寻求帮助的事情：

-需要正确循环的帮助，特别是当用户输入不是整数而是字符时 -当我试图编译时，case语句出现错误，它指向括号，我不知道为什么

该代码应该用从物理课上学到的运动学方程来求解某些变量。这是一种让我习惯C++开始的方法，但是可以使用高级程序员的帮助。 这也是我第一次在stackoverflow上发帖，如果有人对如何正确发帖有一些建议，请告诉我，在我的编程课结束后，会检查是否有任何回复，也会询问我的教授

//Arthur Byra
//27 January 2015
//Program to calculate kinetic equations


/* 
vf = vi + a(t)
x = vi(t) + 1/2(a)(t)^2
vf^2 = vi^2 +2a(s) 

where:

    vi + initial velocity
    vf = final velocity
    s = distance
    a = acceleration (must be constant)
    t = time in seconds
*/

#include<iostream>
#include<cmath>
#include<iomanip>

using namespace std;

int main()
{

    int userInput = 0;
    double initialVelocity = 0;
    double finalVelocity = 0;
    double acceleration = 0;
    double time = 0;
    double deltaDistance = 0;
    char userInputSolveFor;

    cout << "This is a program to calculate certain variables using kinematic equations." << endl;
    cout << "Remember that kinematic equations only work when acceleration is constant!" << endl;
    cout << endl;
    cout << "Which equation did you want to use?" << endl;
    cout << endl;
    cout << "1) vf = vi + a(t)" << endl;
    cout << "2) x = vi(t) + 1/2(a)(t)^2" << endl;
    cout << "3) vf^2 = vi^2 + 2(a)(x)" << endl;
    cout << endl;
    cout << "Input number of the equation you want to use (1,2,3): " << endl;
    cin >> userInput;
    switch (userInput)
    {
        case (userInput == 1):

            cout << "You are using vf = vi + a(t)." << endl;
            cout << endl;
            cout << "What are you trying to solve for?" << endl;
            cout << endl;
            cout << "Use a for acceleration (in m/s/s)." << endl;
            cout << "Use vi for initial velocity (in m/s)." << endl;
            cout << "Use vf for final velocity (in m/s)." << endl;
            cout << "Use t for time (in seconds)." << endl;
            cin >> userInputSolveFor;
            cout << endl;
            switch (userInputSolveFor)
            {
                case (userInputSolveFor == a):

                    cout << "You are solving for acceleration." << endl; //Solving for acceleration
                    cout << endl;
                    cout << "What is the initial velocity (in m/s)?" << endl;
                    cin >> initialVelocity;
                    cout << "What is the final velocity (in m/s)?" endl;
                    cin >> finalVelocity;
                    cout >> "What is the time (in seconds)?" << endl;
                    cin >> time;
                    cout << "The acceleration is " << (finalVelocity - initialVelocity) / time << setprecision(10) << " m/s/s." << endl;
                break;

                case (userInputSolveFor == vi):

                    cout << "You are solving for initial velocity." << endl; //Solving for initial velocity
                    cout << endl;
                    cout << "What is your acceleration (in m/s/s)?" << endl;
                    cin >> acceleration;
                    cout << "What is your final velocity (in m/s)?" endl;
                    cin >> finalVelocity;
                    cout >> "What is the time (in seconds)?" << endl;
                    cin >> time;
                    cout << "The initial velocity is " << finalVelocity / (acceleration * time) << setprecision(10) << " m/s." << endl;
                break;

                case (userInputSolveFor == vf):

                    cout << "You are solving for final velocity." << endl; //Solving for final velocity
                    cout << endl;
                    cout << "What is your acceleration (in m/s/s)?" << endl;
                    cin >> acceleration;
                    cout << "What is your initial velocity (in m/s)?" endl;
                    cin >> initialVelocity;
                    cout >> "What is the time (in seconds)?" << endl;
                    cin >> time;
                    cout << "The final velocity is " << initialVelocity + (acceleration * time) << setprecision(10) << " m/s." << endl;
                break;

                case (userInputSolveFor == t):

                    cout << "You are solving for time." << endl; //Solving for time
                    cout << endl;
                    cout << "What is the acceleration (in m/s/s)?" << endl;
                    cin >> acceleration;
                    cout << "What is the initial velocity (in m/s)?" endl;
                    cin >> initialVelocity;
                    cout >> "What is the final velocity (in m/s)?" << endl;
                    cin >> finalVelocity;
                    cout << "The time is " << (finalVelocity - initialVelocity) / acceleration << setprecision(10) << " seconds." << endl;
                break;

                default:

                    cout <<"The input you have entered is not valid." << endl;
        break;
            }

        case (userInput == 2):

            cout << "You are using x = vi(t) + 1/2(a)(t)^2." << endl;
            cout << endl;
            cout << "What are you trying to solve for?" <<endl;
            cout << endl;
            cout << "Use x for distance (in meters)." << endl;
            cout << "Use vi for initial velocity (in m/s)." << endl;
            cout << "Use t for time (in seconds)." << endl;
            cout << "Use a for acceleration (in m/s/s)." <<endl;
            cin >> userInputSolveFor;
            cout << endl;
            switch (userInputSolveFor)
            {
                case (userInputSolveFor == a):
                    cout << "You are solving for acceleration." << endl;
                    cout << endl;
                    cout << "What is the distance (in meters)?" << endl;
                    cin >> deltaDistance;
                    cout << "What is the initial velocity (in m/s)?" << endl;
                    cin >> initialVelocity;
                    cout << "What is the time (in seconds)?" << endl;
                    cin >> time;
                    cout << "The acceleration is " << deltaDistance - (initialVelocity * time) / (0.5 * pow(time, 2.0)) << setprecision(10) << " m/s/s." << endl;
                break;

                case (userInputSolveFor == vi):

                    cout << "You are solving for initial velocity." << endl;
                    cout << endl;
                    cout << "What is the distance (in meters)?" << endl;
                    cin >> deltaDistance;
                    cout << "What is the acceleration (in m/s/s)?" << endl;
                    cin >> acceleration;
                    cout << "What is the time (in seconds)?" << endl;
                    cin >> time;
                    cout << "The initial velocity is " << (deltaDistance - ((pow(time, 2.0)) * acceleration * 0.5)) / time << setprecision(10) << " m/s." << endl;
                break;

                case (userInputSolveFor == x):

                    cout << "You are solving for distance." << endl;
                    cout << endl;
                    cout << "What is the acceleration (in m/s/s)?" << endl;
                    cin >> acceleration;
                    cout << "What is the initial velocity?" << endl;
                    cin >> initialVelocity;
                    cout << "What is the time (in seconds)?" << endl;
                    cin >> time;
                    cout << "The distance is " << (initialVelocity * time) + ((pow(time, 2.0)) * acceleration * 0.5) << setprecision(10) << " meters." << endl;
                break;

                case (userInputSolveFor == t):

                    cout << "You are solving for time." << endl;
                    cout << endl;
                    cout << "What is the acceleration (in m/s/s)?" << endl;
                    cin >> acceleration;
                    cout << "What is the initial velocity?" << endl;
                    cin >> initialVelocity;
                    cout << "What is the distance (in meters)?" << endl;
                    cin >> deltaDistance;

                    if (initialVelocity == 0):
                    {
                        cout << "The time is " << sqrt(deltaDistance - (0.5 * acceleration)) << setprecision(10) << " seconds." << endl;
                    }
                    else if (acceleration == 0):
                    {
                        cout << "The time is " << (deltaDistance / initialVelocity) << setprecision(10) << " seconds." << endl;
                    }

                break;

                default:
                    cout <<"The input you have entered is not valid." << endl;

        break;
            }

        case (userInput == 3):

            cout << "You are using vf^2 = vi^2 + 2(a)(x)." << endl;
            cout << endl;
            cout << "What are you trying to solve for?" <<endl;
            cout << endl;
            cout << "Use vf for final velocity (in m/s)." << endl;
            cout << "Use vi for initial velocity (in m/s)." << endl;
            cout << "Use a for acceleration." << endl;
            cout << "Use x for distance (in meters)." <<endl;
            cin >> userInputSolveFor;
            cout << endl;
            switch (userInputSolveFor)
            {
                case (userInputSolveFor == vf):

                    cout << "You are solving for final velocity." << endl;
                    cout << endl;
                    cout << "What is the initial velocity (in m/s)?" << endl;
                    cin >> initialVelocity;
                    cout << "What is the acceleration (in m/s/s)?" << endl;
                    cin >> acceleration;
                    cout << "What is the distance (in meters)?" << endl;
                    cin >> deltaDistance;
                    cout << "The final velocity is " << (sqrt(pow(initialVelocity, 2.0))) + (2 * acceleration * deltaDistance) << setprecision(10) << " m/s." << endl;
                break;

                case (userInputSolveFor == vi):

                    cout << "You are solving for initial velocity." << endl;
                    cout << endl;
                    cout << "What is the final velocity (in m/s)?" << endl;
                    cin >> finalVelocity;
                    cout << "What is the acceleration (in m/s/s)?" << endl;
                    cin >> acceleration;
                    cout << "What is the distance (in meters)?" << endl;
                    cin >> deltaDistance;
                    cout << "The initial velocity is " << (sqrt(pow(finalVelocity, 2.0)) / (2 * acceleration * deltaDistance) << setprecision(10) << " m/s." << endl;
                break;

                case (userInputSolveFor == a):

                    cout << "You are solving for acceleration." << endl;
                    cout << endl;
                    cout << "What is the final velocity (in m/s)?" << endl;
                    cin >> finalVelocity;
                    cout << "What is the initial velocity (in m/s)?" << endl;
                    cin >> initialVelocity;
                    cout << "What is the distance (in meters)?" << endl;
                    cin >> deltaDistance;
                    cout << "The acceleration is " << (sqrt(pow(finalVelocity, 2.0)) - (sqrt(pow(initialVelocity, 2.0)))) / (2 * deltaDistance)) << setprecision(10) << " m/s/s." << endl;
                break;

                case (userInputSolveFor == x):

                    cout << "You are solving for distance." << endl;
                    cout << endl;
                    cout << "What is the final velocity (in m/s)?" << endl;
                    cin >> finalVelocity;
                    cout << "What is the initial velocity (in m/s)?" << endl;
                    cin >> initialVelocity;
                    cout << "What is the acceleration (in m/s/s)?" << endl;
                    cin >> acceleration;
                    cout << "The distance is " << (sqrt(pow(finalVelocity, 2.0)) - sqrt(pow(initialVelocity, 2.0))) / (2.0 * acceleration) << setprecision(10) << " meters." << endl;
                break;

                default:
                    cout <<"The input you have entered is not valid." << endl;
        break;
            }

    default:
        while (userInput <= 1 || userInput >= 3)
        {
        cout << "The number you have entered is not valid." << endl;
        cin >> userInput;
        }
    }
    return 0;
}

//亚瑟·贝拉
//2015年1月27日
//动力学方程计算程序
/* 
vf=vi+a（t）
x=vi（t）+1/2（a）（t）^2
vf^2=vi^2+2a（s）
哪里：
vi+初始速度
vf=最终速度
s=距离
a=加速度（必须为常数）
t=以秒为单位的时间
*/
#包括
#包括
#包括
使用名称空间std；
int main（）
{
int userInput=0；
双初始速度=0；
双最终概率=0；
双加速度=0；
双倍时间=0；
双三角距离=0；
char userInputSolveFor；
库特
case（userInput==1）：

您不能使用
开关（）/case:
控制结构来执行此操作。

此外，单个字符不能接受像
vi
或
vf
这样的输入，您需要使用
std:：string userInput；

您实际需要的是一个级联的
if（）/else if（）/else
控制结构，类似这样：

if (userInputSolveFor == "a") {                 
    cout << "You are solving for acceleration." << endl;
    // ...
}
else if (userInputSolveFor == "vi") {
    cout << "You are solving for initial velocity." << endl;
    // ...
}
else if(userInputSolveFor == "vf") {
    cout << "You are solving for final velocity." << endl;
    // ...
}
// a.s.o
else { // <<< That's equivalent to default:
    cout <<"The input you have entered is not valid." << endl;
}

对于
userInput
，这将需要一个
int
类型变量，因此您可能希望在主菜单选择中使用另一个变量（用于等式）。
只要是
case 1:
而不是
case（userInput==1）
，只要您得到“there show a error”您需要告诉我们错误。请检查每个输入：
if（cin>>userInput）{…}else{/*error*/}
更好的问题：你需要发布一个，因为你有几十行与你的错误无关的代码。另一个必须做的是在代码中发布实际的错误消息以及注释，以指示错误出现的位置（我们这里的代码中没有行号）编程技巧：经常编译，尤其是当你对语法不确定的时候。我已经改变了代码的形式，将if和elseif语句包括在内，而不是case和break语句，并且还制作了post-mcve（希望如此）.不知道是否有可能解开这条线，但希望我能找人帮我完成这最后一点errors@ArtByra对你问题的编辑，使得这个答案现在毫无价值。无论如何，据我所知（编译器错误告诉你），你只是缺少了一些右括号
}
。我是如何使你的答案毫无价值的？我将代码的格式更改为您在第一节中建议的格式place@ArtByra这样现在就没人能看到原来的问题了。您想让我恢复编辑吗？--我还修复了第一个错误，我丢失了一个右大括号，但另一个错误仍然存在。
if(cin >> userInput) {
   // ... 
} 
else { 
    /* error */ 
}