Program With Incorrect Answers

[ForTomorrow]

Hi everyone,

I need some help with my C++ code. Here is the problem specification:

"16. In this exercise, you are to create a program that adds, subtracts, multiplies, or divides two integers. The program will need to get a letter (A for addition, S for subtractions, M for multiplication, or D for division) and two integers from the user. If the user enters an invalid letter, the program should display an appropriate error message before the program ends. If the letter is A (or a), the program should calculate and display the sum of both integers. If the letter is S (or s), the program should display the difference between both integers. When calculating the difference, always subtract the smaller number from the larger one. If the letter is M (or m), the program should display the product of both integers. If the letter is D (or d), the program should divide both integers, always dividing the larger number by the smaller one."

And here is the test data. I am posting the results from my desk-check table.

operation first integer second integer answer
A 10 20 30
a 45 15 60
S 65 50 15
s 7 13 6
G -1
M 10 20 200
d 45 15 3
d 50 100 2

Then, I transferred my program into a source file. Here it is:

//Exercise16.cpp - display answer of two integers
//Created/revised by <Patrick> on <October 7 2012>

#include <iostream>
using namespace std;

int main()
{
//declare variables
int firstInteger = 0;
int secondInteger = 0;
int answer = 0;
char operation = ' ';

//enter the operation
cout << "Enter A (addition), S (subtraction), M (multiplication), D (division): ";
cin >> operation;
operation = toupper (operation);

//determine whether the operation is valid
if (operation != 'A' && operation != 'S' && operation != 'M' && operation != 'D')
{
answer = -1;
cout << "Invalid operation: " << endl;
}
else
{
//enter the integers
cout << "First integer: ";
cin >> firstInteger;
cout << "Second integer: ";
cin >> secondInteger;

//calculate the answer
if (operation == 'A')
answer = firstInteger + secondInteger;
else
if (operation == 'S')
if (firstInteger > secondInteger)
answer = firstInteger - secondInteger;
else
if (secondInteger > firstInteger)
answer = secondInteger - firstInteger;
else
if (operation == 'M')
answer = firstInteger * secondInteger;
else
if (operation == 'D')
if (firstInteger > secondInteger)
answer = firstInteger / secondInteger;
else
if (secondInteger > firstInteger)
answer = secondInteger / firstInteger;
//end if
//end if
//end if
//end if
//end if
//end if
//end if
//end if
}//end if

//display the answer
cout << "Answer: " << answer << endl;

system ("pause");
return 0;
} //end of main function

After putting in the data, everything worked fine, except the last two operations, which are M (multiplication) and D (division). All the answers for the last two operations essentially give me a 0.

I would like to know where I went wrong. Hopefully, someone can help me figure out what is wrong.
Please, respond to this thread as soon as possible.