/* This program demonstrates:
 * 1. Using cout to print literals, variables and text prompts for clarity
 * 2. Declaring, initializing and using variables of different primitve types
 * 3. The char type for single character data
 * 4. The 3 other integer types - short, int and long
 * 5. Different ways of representing an integer - decimal, octal, hexadecimal
 * 6. The 2 major floating point types - float and double
 * 7. Fixed and scientific notations for floating point numbers
 * 8. The cin object, used to read values into a variable.
 *
 * Variables:
 * Declaring a variable is us telling C++ to make room in memory to
 * hold a value. Variables have 5 properties - name, type, size, value
 * and address.
 * The name of a variable is an identifier. Follow rules and conventions
 * for naming identifiers.
 * The identifier is just the "word" we use to refer to the value in
 * the variable. Conventionally, it makes sense in context, but it doesn't
 * have to, in order to just produce the required output.
 * Initialization is giving the variable its first value, this value may
 * change later. If we do not initialize variables, the leftover "junk"
 * value might bleed into our program and produce the wrong result.
 */
#include <iostream>
using namespace std;

int main()
{
    /* bool is the C++ boolean type. It can only hold one of two values:
     * true and false.
     * 0 is interpreted as "false", Anything not 0 is "true"
     * C++ will print 1/0 instead of true/false
     * "true" and "false" are c++ keywords.
     */
    bool ans;
    ans = true;
    cout<<"ans = "<< ans << endl;

    /* The char type is an integer type that can be used to store
    * single characters. The character stored in a char variable
    * must be in single quotes. The value in the char variable is
    * not associated in any way with the name of the variable.
    * Any single keystroke character can be stored in a char variable
    */
    char letter;            // declaration
    letter = 'B';           //initialization
    cout<<"letter: "<<letter<<endl;

    /* The range of a char is -128 to + 127. If we give it a value out of
     * range, it will ompile and run but produce unintelligible output.*/
    letter = 832583254890997;
    cout<<"letter is now "<<letter<<endl;

    /* The point of a variable is that it can change values through the
     * course of a program.
     * The following line changes the value in letter from whatever it was
     * set to previously, to 's'
     */

    letter = 's';
    cout<<"Changed letter: "<<letter<<endl;

    /* The cin statement is the opposite of cout. It takes values from the screen
     * and brings it into the program. The arrows point towards the variable.
     * Whatever number the user typed is stored in the variable.
     * We need to wait till the user presses Enter or enters some whitespace, for
     * the trasfer to happen.
     * If we just use cin, then the cursor is going to blink, waiting for
     * user input. However, the user does not know what to do. So, it is
     * standard practice to "prompt" the user. A prompt is a cout statement
     * that tells the user about the computer's expectations. */
    cout<<"Enter a character: ";        //prompt
    cin>>letter;

    cout<<"User entered: "<<letter<<endl;

   /* There are 3 integer types - short, int and long
    * int is considered the "standard" type for numeric values without fractional
    * parts. ints occupy 4 bytes in memory.
    * shorts are smaller ints, occupying 2 byes. longs are bigger ints, occupying
    * 8 bytes.
    * All 3 of these, and char, are incapable of holding fractional parts.
    */
   int num = 1276;          // usually the default "integer" type
   short smallNum = 20000;  // For "smaller" numbers, up to 32000
   long bigNum = 546546764646465798;    // can hold up to 18 digits

    /* Escape sequences are certain characters, that, when preceded by the backslash
     * character, has a special meaning when printed. For example, in the folowing
     * lines, \n will print as a new line */

    cout<<"num: "<< num <<"\nsmallNum: "<<smallNum<<"\nbigNum: "<<bigNum<<endl;

    /* C++ understands 3 ways of representing integers. The usual "human-readable"
     * way is the decimal representation, which has 10 different digits 0-9
     * It is also possible to represent integers in octcal or hexadecimal systems.
     * Octal numbers only use the digits 0-7, and must be prefaced with a 0
     * Hexadecimal numbers use 16 different digits: 0-9 and the A, B, C, D, E,
     * and F to reperesent a face value of 10, 11, 12, 13, 14, and 15 at that digit
     * Hexadecimal numbers must be prefixed with 0x */

    num = 191;          //decimal
    smallNum = 031;     //octal
    bigNum = 0x48A;     // hexadecimal

    //The following line will print the decimal representation of the numbers above

    cout<<"num: "<< num <<"\nsmallNum: "<<smallNum<<"\nbigNum: "<<bigNum<<endl;

    /* Floating Point literals (numbers with fractional parts) can be represented
    * in fixed (normal) notation or scientific notation.
    * Scientific notation is the way of writing the number with only 1 digit before the
    * decimal point, followed by 10 raised to an exponent.
    * However, instead of writing 6.023 x 10 ^ 23, we will write
    * 6.023e23
    * Here, "e" indicates the exponent of 10. There no spaces while specifying
    * the number.
    */

    float fraction;
    fraction = 45.2963;      // fixed notation
    double electronCharge = 1.8e-19;    //scientific notation

    cout<<"fraction: "<<fraction<<"\nelectronCharge: "<< electronCharge<<endl;

    /* We can do math and store the result in variables. For example, the next 3
     * lines read the side length of a square from the user and calculate its area */

    double sideLength;
    cout<<"Enter side length of the square: ";
    cin>>sideLength;
    double area = sideLength * sideLength;
    cout<<"The area is "<<area<<endl;
    return 0;
}