invalid input by the user - c++

Question

hey guys so this is my program, I need to notify the user that if hhe/she enters a letter other than w d b or w that is an invalid request. what ive done so far does this, but when i input a number to the dollars_withdraw or dollars_deposit or account_balance the program will do the transaction but also add the "invalid request" before going back to main loop. how do i change it so the program wont do that for numerical inputs for the withdraw deposit and balance?:
// Atm machine.cpp : Defines the entry point for the console application.
#include <iostream>
#include <string>
using namespace std;
int main ()
{
char user_request;
string user_string;
double account_balance, dollars_withdraw, dollars_deposit;
account_balance = 5000;
while(account_balance >0)
{
cout << "Would you like to [W]ithdraw, [D]eposit, Check your [b]alance or [Q]uit?"
<< endl;
cin >> user_string;
user_request= user_string[0];
if(user_request == 'w' || user_request== 'W')
{
cout << "How much would you like to withdraw?" << endl;
cin >> dollars_withdraw;
if (dollars_withdraw > account_balance || dollars_withdraw <0)
cout << "Invalid transaction" << endl;
else
account_balance = account_balance - dollars_withdraw;
cout << "Your new balance is $" << account_balance << endl;
}
if (user_request == 'd' || user_request== 'D')
{
cout << "How much would you like to deposit?" << endl;
cin >> dollars_deposit;
if (dollars_deposit <0)
cout << "Invalid transaction" << endl;
else
account_balance= account_balance + dollars_deposit;
cout << "Your new balance is $" << account_balance << endl;
}
if(user_request == 'b' || user_request == 'B')
{
account_balance= account_balance;
cout << "Your available balance is $" << account_balance << endl;
}
if(user_request == 'q' || user_request == 'Q')
break;
else
cout << "Invalid request " << endl;
}
cout << "Goodbye" << endl;
return 0;
}

Answer 1

Sure it does. Your code says:
If it is a 'w' do something
...
If it is a 'q' do something, else yell "invalid"
So if the user does not enter a 'q', the last 'else' block will always be executed. Either use else if throughout or change your code to use a switch statement:
// Either:
if (user_request == ...) {
...
} else if (user_request == ...) {
...
} else {
std::cout << "invalid";
}
// Or (better, faster):
switch (user_request) {
case 'q':
case 'Q':
...
break;
...
default:
std::cout << "Invalid request";
}
A third option would be to use continue:
while (...) {
user_request = ...
if (user_request == 'w' ...) {
...
continue; // In this iteration, no other code within the while loop is executed.
}
if (...)
...
}

Answer 2

This is a bad programming practice. Please use Switch Case for what you need to achieve. And put a "break" statement after every case branch.

Answer 3

chain your if statements into if, else-if, else-if, ..., else.

Answer 4

else statements only "know of" the if statement immediately previous. For example:
if (myNumber == 0)
{
// Triggers when myNumber is zero.
}
if (myNumber == 1)
{
// Triggers when myNumber is one.
}
else
{
// Triggers when myNumber is not one.
}
This can be fixed with else if statements. In your case it would look something like this:
if (user_request == w)
{
// ...
}
else if (user_request == d)
{
// ...
}
// ...
else cout << "Invalid request.";

Answer 5

In my old CS class, I'd do things like this:
string user_string;
do {
if(user_string) cout << "Enter a valid value!" << endl;
cin >> user_string;
} while(user_string != "w" && user_string != "d");

Answer 6

You need to use else if as follows:
if(user_request == 'w' || user_request== 'W')
{
...
} else if(user_request == 'd' || user_request== 'D')
{
....
} else if(user_request == 'b' || user_request== 'B')
{
.....
} else if(user_request == 'q' || user_request== 'Q')
{
...
} else
{
// Invalid request
}