C++ 银行项目；如何从文件中读取字符串转换为 float 并求和

Question

问题陈述:读取客户支票账户信息的 C++ 程序计算他/她的账户余额。应开发基于菜单的应用程序以迭代执行以下功能，直到用户请求退出程序:1. 显示，2. 存款，3. 取款，4. 退出。

这就是我目前所拥有的。

#include <iostream>
#include <fstream>
#include <iomanip>
#include <string>
using namespace std;

//Main function
int main()
{ 
    //Identify type variables
    int x=0;
    float amountinput,famount,sum;
    string firstname, lastname,date,filename,input,ID,amount;
    fstream file;
//Program loop
    while(true)
    {
        //Main menu loop
        do
        {

        cout<<"Enter the number of the option you would like carried out.\n";
        cout<<"1. Summary\n";
        cout<<"2. Deposit\n";
        cout<<"3. Withdraw\n";
        cout<<"4. Quit\n";
        cin>>x;
    }
    while(!x);

    //When Quit is input, break
    if(x==4)
    {
        break;
    }
        //Summary display
        if (x==1)
        {
            cout<<"You have selected option number 1. Summary.\n"<<endl;
            cout<<"Enter your Cust_ID: "; 
            cin>>ID;
            file.open("C:\\Users\\Raggulddon\\Desktop\\C++ supplement
                       \\Cust_"+ID+".dat", ios::in|ios::out|ios::app);

            //IF not found error.
            if(!file)
            {
                cout<<"Sorry your account could not be found\n";
            }
            //Else display all content.
            else
            {
                    cout<<endl<<file.rdbuf()<<"\n";
                    file.close();

            }           
        }
        //Deposit
        else if(x==2)
        {
            cout<<"You have selected option number 2. Deposit.\n";
            cout<<"Please enter you account ID: ";
            cin>>ID;
            file.open("C:\\Users\\Raggulddon\\Desktop\\C++ supplement
                        \\Cust_"+ID+".dat", ios::in|ios::out|ios::app);

            if(!file)
            {
                cout<<"Sorry the requested account could not be located.\n";
            }
            else
            {
            file>>firstname>>lastname;
            cout<<endl<<firstname<<" "<<lastname<<endl; 
                while(!file.eof())
                {
                    file>>date>>amount;
                    //
 %%%%%%%%%%%%%%%%%%%//This is mainly where I am missing the lines of code..
                    //                      
                    float atof(string& amount);
                    cout<<date<<"\t\t"<<amount<<endl;
                }


                    cin.get();cin.get();
                cout<<"How much would you like to deposit today.";
                cin>>amountinput;

                cout<<endl;
                file.close();

            }
        }

            else if(x==3);
            else if(x==4);


}       
cin.get();cin.get(); //or system("PAUSE");
return 0;
}

示例文本文件如下所示，但行数不同。

James Bond
01/01/12 200010
03/30/12 -40000
04/30/12 -40000
05/30/12 -40000
06/30/12 -40000
07/30/12 -40000

我已设置 amount = string，然后我希望每个字符串彼此独立(以便我可以添加它们)并将它们转换为 float 或 double，以两者为准。

基本上，是这样的:

fstream file;
do
file>>date>>amount++; //I know this doesn't work, what will..
while(!file.eof());
float deposit;
finalAmount= deposit+amount;

Answer 1

C++ 输入运算符 >> 的好处在于它可以接受不同类型的参数，例如一个 double:

std::string date;
double amount;

file >> date >> amount;

但是，我更推荐使用 std::getline和 std::istringstream解析它:

std::string line;
std::getline(file, line);

std::istringstream iss(line)
iss >> date >> amount;

---

在某种程度上相关的注释中，不要使用while (!file.eof())。 eof 标志在实际输入操作失败之前不会被设置，因此除非您检查循环内的错误，否则您将尝试读取一次到多次。

而是做例如

while (std::getline(file, line))
{
    ...
}