/* This program demonstrates
 * 1. Fall through and character inputs for a switch statement
 * 2. sizeof operator
 * 3. unsigned qualifier
 * 4. Working with characters
 * 5. Conditional Operator
 * 6. The while loop
 * 7. Looping on Error Input
 *
 *  Using character variables
 * A char variable is an integer type, so it can be assigned integer values. However,
 * doing so might result in unexpected behavior, since the numbers translate to
 * different characters using an internal code (ASCII - to be covered later).
 *
 * To assign a character value to a char variable, we need to pace the character
 * in single quotes.
 * Single quotes char values can only be a single charcater or in certain cases,
 * an escaped character (ones  that begin with \, followed by a character.
 *
 * Using if/switch statements with char variables
 * char variables might be used in boolean expressions just like ints and doubles.
 * The only difference is that chracter literals must be a single chracter or an
 * existing escape sequence, enclosed in single quotes.
 *
 * The Conditional operator
 * A simple if-else statement with ONLY ONE LINE in the if block and the
 * else block can be written using the conditional operator.
 * The conditional operator is the only ternary operator (operator with 3
 * operands) we'll cover in this course.
 * This is the syntax:
 * (condition used for the if) ? line in the if block : line in the else block;
 *
 * while loops
 * while loops are the first type of loop. It checks the condition first.
 * If true, the loop body is executed. If false, it skips over the loop body
 * and goes to the line after the loop.
 *
 * Looping on Error Input
 * This continues on from the 3 methods of validating user input in
 * conditionals.cpp. Even if we ask the user to enter the corrected
 * value, there is no guarantee that the user would follow instructions.
 * It would be better if we can loop until the user gives us a value that
 * we can work with.
 *
 */

#include <iostream>
using namespace std;
int main()
{
    /* The following example will read in a character representing a month and print the
	 * name of the month and the number of days in that month in a standard calendar year.
	 * This demonstrates how to use a char variable in a switch statement. The case labels
	 * need to be single quoted.
	 */
    char month;
    cout<<"Enter the month (letter): ";
    cin>>month;
    int daysInMonth=0;
    switch(month)
    {
        case 'F': daysInMonth=28;       // February
            break;
        case 'A':                       // April
        case 'j':                       // June
        case 'S':                       // September
        case 'N': daysInMonth=30;       // November
            break;
        case 'J':                       // January
        case 'M':                       // March
        case 'm':                       // May
        case 'U':                       // July, since both J's were taken already
        case 'a':                       // August
        case 'O':                       // October
        case 'D': daysInMonth=31;       // December
            break;
        default: cout<<"Invalid month"<<endl;
    }
    if(daysInMonth !=0)     // quick check to see if there is a valid number of days to print
        cout<<"Days in month: "<<daysInMonth<<endl;

    /* Just because a char variable is called 'a' doesn't mean its value
     * is automatically 'a'.
     * We can read in chars with a cin
     * We can compare and work with chars just like ints and doubles as long as
     * char literals are enclosed in single quotes.
     */
    char a = '!';
    cout<<"a: "<<a<<endl;
    cout<<"Enter a character: ";
    cin>>a;
    cout<<"User entered: "<<a<<endl;

    if(a == 'A')
        cout<<"The variable \"a\" holds the value: \'A\'"<<endl;
    else cout<<"The variable \"a\" does not hold the value: \'A\'"<<endl;
    /* The sizeof operator gives us the size (in bytes) of a dtat type or a variable */
    int num1;
    cout<<"The size of num1: "<< sizeof(num1)<<" bytes"<<endl;
    cout<<"Size of doubles: "<< sizeof(double)<<" bytes"<<endl;

    /* Typically, the numeric types can store both positive and negative values. However, this
   * reduces the largest/smallest numbers we can store in the variable to half the domain size.
   * If we're sure that the value in a variable will only be positive, we can make use of the
   * entire domain size, by qualifying the variable as "unsigned"
   */

    num1 = 0xFFFFFFF9;  // value close to 2 ^ 32
    // count of possible values: 2^32
    // range: -2^31 : 2^31 -1

    cout<<"Signed int: "<< num1<<endl; // will print a negative number, since value is greater than 2^31-1

    unsigned num2 = 0xFFFFFFF9; // store the same value in an unsigned int variable
    // count of possible values: 2^32
    // range: 0 : 2^32 -1

    cout<<"Unsigned int, num2: "<<num2<<endl;    // will print the actual value
	
	 /* the conditional operator can be nested.
     * The lines below use the conditional operator in both the "True"
     * and "False" parts of the outer conditional statement.
     * We can thus, use the nexted conditional operator to get the
     * largest of 3 numbers.
     */
    int x,y,z,largest;
    cout<<"Enter 3 numbers: ";
    cin>>x>>y>>z;

    (x>y) ? (x>z) ? largest = x : largest = z : (y>z) ? largest = y : largest = z ;

    cout<<"Largest number is "<<largest;
	
	 /* Print the frst 200 natural numbers 1 - 200
    * Step 1: Start at 1
    * Step 2: Check if we're done/not done. If done, go to step 4
    * Step 3: Print the number
    *        Move to next number - increment
    *        Go back to step 2
    * Step 4: Move on
    */
   cout<<"Before the while loop"<<endl;
   int i = 1;       // Step1 - initialization
   while ( i <= 200)    // Step 2 - loop condition
   {
       cout<<i<<endl;   // Step 3is - loop body
       i++;             // increment
   }
   cout<<"After the while loop"<<endl;

   cout<<"Before the do-while loop"<<endl;
   i = 1;
   do
   {
       cout<<i<<endl;
       i++;
   }while (i<=200);

   cout<<"After the do-while loop"<<endl;
	
	/* Input validation - Method 4 - Looping on an error input
     * We want a valid grade between 0 and 100, so we loop as long as the user keeps
     * entering numbers not in the range.
     * Please note that the initial read, the check and the next read are
     * all done with the same variable
     */
    cout<<"Method 4 of input validation - Looping on an error"<<endl;
	double grade;
	cout<<"Enter a grade: ";
	cin>>grade;
    while ( grade< 0 || grade > 100  )	// invert the condition for a "valid" grade
    {
        cout<<"You entered an invalid grade. Please enter a grade between 0 and 100: ";
        cin>>grade;		// next read - increment
    }

    if (grade >= 70)
		cout<<"Pass"<<endl;

    return 0;
}