/* This program demonstrates
 * 1.  Working with characters
 * 2. Conditional Operator
 * 3. Validating Use Input
 * 4. While loops
 *
 *  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
 *
 * Input validation
 * When we get inputs from the user, we have to make sure the inputs make sense
 * from the perspective of the problem statement. For example, if we want to
 * perform division, the divisor must not be 0.
 * When we get inputs, we should not assume the user is aware of these limitations,
 * and check for violations. This is called algorithmic error checking.
 * There are different approaches to this, including, but not limited to:
 * a. Printing an error message
 * b. Correcting the wrong entries in the program
 * c. Asking the user to correct the wrong entry
 * d. Looping on an error input
 *
 * Loops:
 * Loops are repetitive statements. They execute the same lines of code
 * over an over again, as long as a certain condition is true.
 * The first type of loop is the while loop. "while" is a keyword.
 * A loop has 4 parts: initialization, condition, loop body and increment.
 *
 * 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.
 *
 */
#include <iostream>
using namespace std;
int main()
{
	/* 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 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;
	
	 /* Validating user input - making sure the user's input can be used in
     * the problem without causing issues - either from C++'s perspective
     * or, from the problem's perspective.
     * For this example, we're going to ask the user to enter a grade. If
     * the grade is at least 70, the student passes.
     * A valid grade is between 0 and 100.
     */
    double inputGrade;
    cout<<"Enter the grade: ";
    cin>>inputGrade;

    /* validate user input - with an error message
    * If the grade is below 0 or above 100, print an error message. Otherwise,
    * check if the student passed
    */
    cout<<"<=Method 1 : print an error message"<<endl;

    grade = inputGrade;

    if ( grade < 0 || grade > 100)
    {
        cout<<"Error. Invalid grade entered"<<endl;
    }
    else
    {
        if(grade >= 70)
            cout<<"Passing grade"<<endl;
        else cout<<"Try again"<<endl;
    }

    /* Method 2 - default to value
     * If grade < 0 - set grade to 0
     * If grade > 100, set grade to 100
     */
     cout<<"Method 2 - default to value"<<endl;
    grade = inputGrade;
    if(grade < 0)
        grade = 0;
    else if (grade >100)
        grade =100;

    if(grade >= 70)
        cout<<"Passing grade "<<endl;
    else cout<<"Try again"<<endl;

    /* Method 3 - Get a correction
     * If error, ask the user for anothr value
     */
    cout<<"Method 3 - get a correction"<<endl;
    grade = inputGrade;
    if(grade <0 || grade >100)
    {
        cout<<"Error. Grade should be between 0 and 100. Enter the correct grade: ";
        cin>>inputGrade;
    }
        grade = inputGrade;

    if (grade >= 70)
        cout << "Passing grade" << endl;
    else cout << "Try again" << endl;
	
	/* Method 4 - Looping on an error input
     * We want an odd number, so we loop as long as the user keeps
     * entering even numbers.
     * 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;
	grade = inputGrade;
	
    while(grade <0 || grade >100)
    {
        cout<<"Error. Grade should be between 0 and 100. Enter the correct grade: ";
        cin>>grade;
    }
    
    if (grade >= 70)
        cout << "Passing grade" << endl;
    else cout << "Try again" << endl;
	
	/* 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;

    return 0;
}