#include <iostream>
using namespace std;

#define C_STYLE_PI 3.1415926

int main()
{
    // use const to define constants that never
    //    (or rarely) change
    const double PI = 3.1415926;

    // constants do not change unless we recompile the code
    const double interest_rate = 0.09;

    double balance = 100.0;

    // subtract withdrawal amount
    double amount;
    cout << "Enter ATM Withdrawal Amount: ";
    cin >> amount;

//    balance = balance - amount;
    balance -= amount;

    // add earned interest
//    balance = balance * (interest_rate + 1);
//    balance *= interest_rate + 1;
    balance += balance * interest_rate;

    cout << "You earned some interest!  Total balance: $";
    cout.precision( 2 );
    cout.width( 20 );
//    cout.width( -20 );   // left justify
    cout.fill( 'a' );
    cout << balance << endl;

    // float -- typically has 7 digits of accuracy
    // double -- typically has 14 digits of accuracy
    
#if 0
    int x, y;     // these lines are commented out
    y = x + 10;
    cout << y << endl;
#endif

    char answer;
    cout << "Do you want to know what your balance is? (y/n): ";
    cin >> answer;
    cout << "You entered '" << answer << "'\n";

//    if ( condition ) {
//      code-to-run-if-condition-is-true
//    }

    // operator  ==  is the test for equality
    // operator  !=  is the test for inequality
    // operator  >  >=  <  <=
    if ( answer == 'y' ) {
        cout << "Okay, your balance is $" << balance << endl;
    } else {
        cout << "Okay, no balance for you." << endl;
    }

//    if ( condition ) {
//      code-to-run-if-condition-is-true
//    } else {
//      code-to-run-if-condition-is-false
//    }

    // LOOK OUT!  Don't use = when you mean ==
    if ( answer = 'y' ) {
        cout << "STILL ANSWERED 'y'" << endl;
    }

//  A "condition" is a true/false value (boolean or bool)
//  In C++, false == 0  and  true == non-zero

    int x = 10, y = 20;

    if ( x > 0 ) {
        cout << "x is greater than 0.\n";
    }

    // use && to mean Logical-AND
    if ( x > 0  &&  y > 0 ) {
        cout << "both x and y are greater than 0.\n";
    }

    // use || to mean Logical-OR
    if ( x > 100  ||  y > 0 ) {
        cout << "x is greater than 100  OR  y is greater than 0.\n";
    }

    // compound condition is evaluated left-to-right
    // and it stops (short-circuits) if possible
    if ( x > 100  &&  y > 0 ) {
        cout << "x is greater than 100  AND  y is greater than 0.\n";
    }

    if ( x + y > 25 && x > 0 ) {
        cout << "This ought to be true.\n";
    }


//  if-else chain:
//
//    if ( condition1 )
//    {
//      code-to-run-if-condition1-is-true
//    }
//    else if ( condition2 )
//    {
//      code-to-run-if-condition2-is-true
//    }
//    else if ( condition3 )
//    {
//      code-to-run-if-condition3-is-true
//    }
//    else  // catch-all default case
//    {
//      code-to-run-if-all-conditions-are-false
//    }

    double grade = 87.5;
    char letter_grade;

    if ( grade >= 90.0 )
    {
        letter_grade = 'A';
    }
    else if ( grade >= 80.0 )
    {
        letter_grade = 'B';
    }
    else
    {
        letter_grade = 'F';
    }

    return 0;
}