/* This program demonstrates
 * 1. Random number Generation
 * 2. Working with numbers and digits
 * 3. Introduction to arrays
 * Random Number generation.
 * We can use the rand() function in the cstdlib library to generate a random
 * number. It will return an integer. We can set an upper limit by calling the
 * random function and then using the modulus on the returned value.
 * We can set a lower limit by adding the lower limit to the value returned by
 * the function.
 *
 * Arrays
 * An array is a collection of variables that satisfies the following properties:
 * 1. All the variables in the array are of the same type.
 * 2. All the variables share the same name and are accessed by an index.
 * 3. The elements (individual variables) are ordered and start at index 0.
 * 4. The elements are in continuous memory locations.
 *
 */

#include<iostream>
#include<cmath>
#include<cstdlib>        //for the rand() function

using namespace std;

int main()
{
    // The rand() function generates a random integer btween 0 and 2^31
    cout << rand() << endl;

    int init;

    cout << "Enter a seed value for the RNG: ";
    cin >> init;


    /* The srand() function initializes the RNG. If we do not initialize it,
     * it would generate the same sequence of numbers each time.
     * Here, we ask the user for a number, and initialize the RNG with the
     * user entered value. Conventionally, we use the system time, but we don't
     * do that here, since different platforms need different libraries for that.
     */
    srand(init);
    int low = 25, high = 120;
    // generate 10 random numbers  in a range - low => 15, high => 120
    // rand() % (high - low) + low
    for (int i = 0; i < 10; i++)
        cout << rand() % (high - low) + low << endl;
    
    int num;
    cout<<"Enter a number: ";
    cin>>num;
    /* to count the number of digits in a number: 
     * We keep dividing by 10. Every time we do that, we remove the last digit. 
     * If the number is not 0, then there are more digits, so count 1 digit. 
     * Repeat until the number becomes 0
     */
    int numDigits = 0;
    while(num != 0)
    {
        numDigits ++;
        num = num / 10;
    }
    cout<<"Number of digits: "<< numDigits<<endl;
    
    
    /* We declare an array similar to how we declare a variable, with the
    * notable difference being the array index operator "[]" attached to
    * the array's name, with the array size specified.
    * While declaring, the array's size HAS TO BE AN INTEGER LITERAL OR
    * CONSTANT.
    * We can also declare and initialize an array using set notation
    * If the array is small enough, and we know, for sure, what values
    * are in the array, we can use set notation
    */
    const int NUM = 10;
    int array[NUM] = {4, -9, 13, 25, -76, 1, 2, 3 };
    /*We cannot split this up into 2 lines, like we could for single variables.*/

    /* If we don't give it enough values, the array is filled out with 0's
     * If we give too many elements, it will cause an error
    int numbers[5] = {1,2,3,4 ,5,6,7,8}; //error
     */

    /* If we try to print an array using just its name, it would print the
     * starting address of the array. To get to an individual element, we
     * need to specify the array name and the index, using the [] notation
     */
    cout<<"Element in index 2: "<< array[2]<<endl;
    cout<<"The array is "<<array<<endl;

    /* To print an entire array, we would need a loop iterating through the
     * elements of the array
     */
    for(int i=0; i< NUM; i++)
    {
        cout<< array[i]<<"\t";
    }

    //accept array values from the user
    cout<<"\nEnter values for the array: ";
    for(int i=0; i<NUM; i++)
    {
        cin>>array[i];
    }

    cout<<"Enter the element at index 4: ";
    cin>>array[4];
    return 0;
}