Multiple 'if' statements without an 'else' - c++

Question

The code I have to write is basically a mini bank. It asks for an initial amount, the type of action, and a second operator for that action.
I'm not allowed to use else, but am allowed to use if statements (I don't understand why), nor am I allowed to use a loop or an array.
This is the code I have so far:
#include <iostream>
#include <iomanip>
#include <string>
using namespace std;
int operand1;
int operand2;
float output;
char action;
int main()
{
cout << fixed << showpoint << setprecision(2);
cout << "Enter the initial balance [1-1000]: " << endl;
cin >> operand1;
cout << "Enter an action (D, W, I or C):" << endl;
cin >> action;
cout << "Enter the second operand:" << endl;
cin >> operand2;
if ((action != 'D' && action != 'W' && action != 'I' && action != 'C') || (operand1 > 1000 || operand1 < 1) ||
(action == 'I' && operand2 > 15 || operand2 < 1) || (action == 'C' && operand2 != 20 && operand2 != 10 && operand2 != 5) ||
(operand2 > 1000 || operand2 < 1))
{
cout << "Input out of range" << endl;
return 0;
}
if (action == 'D')
{
output = (operand1 + operand2);
cout << "The new account balance is " << output << endl;
}
if (action == 'W')
{
output = (operand1 - operand2);
if (output<0)
{
cout << "Input out of range" << endl;
return 0;
}
cout << "The new account balance is " << output << endl;
}
if (action == 'I')
{
output = ((float)operand1 + (((float)operand2 / 100) * (float)operand1));
cout << "The new account balance is " << output << endl;
}
if (action == 'C')
{
output = operand1 % operand2;
cout << operand1 / operand2 << " bills dispensed plus " << output << endl;
}
cin.get();
cin.get();
return 0;
}
On certain instances, I get multiple errors instead of just one. For example:
Enter the initial balance [1-1000]: 1030
Enter an action (D, W, I or C): D
Enter the second operand: 40
Input out of range
However, it seems to just move on when it sees the error anyway, and I get this output:
Enter the initial balance [1-1000]:
1030
Input out of range
Enter an action (D, W, I or C):
D
Enter the second operand:
40
The new account balance is 1070.00
I can't seem to figure out how to have only one output, and for it to just display the error with no balance, without using an else statement.

Answer 1

Use switch (action):
https://en.cppreference.com/w/cpp/language/switch
After the cases it can have a default.
Also lots of conventions forbid else, but not forbid elseif - are you sure elseif is forbidden in your case?
But even if elseif is allowed - switch is better to read and is a more elegant solution.

Answer 2

You can use switch by taking all the commands as different cases. This is what others have already said.
My contribution would be that you could put your first if statement i.e. the error case under the default case.
And before using switch statements, could you check if it is ever explicitly stated that you can't use 'else if' statements. If not, you should use that. It is not the same as an 'else' statement.

Answer 3

&& has a higher precedence than ||
if (
(action != 'D' && action != 'W' && action != 'I' && action != 'C') ||
(operand1 > 1000 || operand1 < 1) ||
// (action == 'I' && operand2 > 15 || operand2 < 1) ||
(action == 'I' && (operand2 > 15 || operand2 < 1)) ||
(action == 'C' && operand2 != 20 && operand2 != 10 && operand2 != 5) ||
(operand2 > 1000 || operand2 < 1))
{
cout << "Input out of range" << endl;
return 0;
}
To have more traceability, on what the code does, it would be worth the effort to do:
if (action != 'D' && action != 'W' && action != 'I' && action != 'C')
{
cout << "Input out of range; action " << action << endl;
return 0;
}
if (operand1 > 1000 || operand1 < 1)
{
cout << "Input out of range; 1st operand: " << operand1 << endl;
return 0;
}
...