+= operators , -=operators

[DesmondLee]

Hello There. Can someone help me to modify my program so that the add opperations is

+ = operators & - = operators ?

 #include<iostream>
#include<cmath>
using namespace std;

int inputoption();

int inputoption()
{
	char option;
	cout<<"Your opening balance is RM1000.00"<<endl;
	cout<<"Enter any one of the following options: "<<endl;
	cout<<"0.\tQuit"<<endl;
	cout<<"1.\tDeposit"<<endl;
	cout<<"2.\tWithdrawal"<<endl;
	cout<<"3.\tBalance"<<endl;
	cout<<"Your option: ";

	do
	{
		cin>>option;
		if(option!='0' && option!='1' && option!='2' && option!='3')
		{
			cout<<"Invalid option." <<endl;
			cout<<"Pleae enter again." <<endl;
		}
	}
	while(!(option>='0' && option<='3'));
	return option;
}
int main()
{
	double const opb=1000.00;
	double cb=0;
	double amount;
	int userchoice;
	userchoice=inputoption();
	do
	{
    if (userchoice=='0')
	{
		break;
	}
	else if(userchoice=='1')
	{
		cout<<"Amount to Deposits: RM ";
		cin>>amount;
		cb=opb+amount;
	}
	else if(userchoice=='2')
	{
		cout<<"Amount to Withdraw: RM ";
		cin>>amount;
		cb=opb-amount;  
		while(cb<=10.00)
		{
		cout<<"Sorry, a minumum balance of RM10.00 is required."<<endl;
		cout<<"Please enter a new amount or 0 to quit."<<endl;
		cout<<"Amoun to Withdraw: RM ";
		cin>>amount;
		cb=opb-amount;
		}
	}
	else if(userchoice=='3')
	{
		cout<<"Your current balance is RM "<<cb<<endl;
	}	
	cout<<"Your current balance is RM "<<cb<<endl;
	}while(true);
	system("pause");
	return 0;
}

[boost lexical cast]

variable += value is variable = variable + value.

Doesn't work with your program.