/* This program demonstrates
 * 1. While loops
 * 2. do-while loops
 * 3. Looping on invalid input
 * 4. Counting loops
 * 5. Counting down and accumulation
 *
 * 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.
 *
 * do - while loop
 * The do-while loop is the second kind of loop
 * this loop checks the condition AFTER executing the loop body, when the
 * while loop checks the condition BEFORE executing the loop body.
 * So, the do-while executes the loop body AT LEAST ONCE.
 * Otherwise, the while loop and the do-while can be written in terms of the other
 *
 * 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.
 *
 * ccumulation
 * Most of the time, we have to accumulate an operation.
 * For example, we want to add a bunch of numbers.
 * Accumulation is the process of keeping a running result.
 * For example, we might need to add all the numbers the user enters, stopping
 * at the first negative number. However, we can only add 2 numbers at
 * a time. So, we add the first number to the sum, then we add the next
 * number to the sum and store the result back in the sum, and we repeat
 * this process until we have added in the last number.
 */

#include<iostream>
using namespace std;
int main()
{
    /* Print the first 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;

    // Same problem, solved with a do-while loop
    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;

    /* Accumulation
     * "collecting" a series of values into 1 variable - build off update
     * Problem Statement - Calculate the cumulative class participation grade over 4 weeks
     * Step 1:  Initialize a sum variable to 0, and a counter to 4.
     *          Also declare a weekly grade variable.
     * Step 2:  We're counting down here, so check if the number of weeks
     *          left (counter) is over 0
     *          Step 2.a: Read the weekly value
     *          Step 2.b: Add value to the sum
     *          Step 2.c: Decrement the counter
     *          Step 2.d: Go back to step 2
     * Step 3: Print the total
     */
    int weekly=0, total=0, numWeeks=4;
    while(numWeeks>0)
    {
        cout<<"Enter the weekly grade: ";
        cin>>weekly;
        total = total + weekly;
        numWeeks--;
    }
    cout <<"The total is : "<<total<<endl;
    return 0;
}