Is this necessary?

A simple program I did for completing an exercise:

Code:

 //This program reads the <char> from the keyboard,  and then displays one of the following messages:/* 1. If <char> is a lower case letter, the message is 
           "The upper case character correspond to <char> is ___. "
   2. If <char> is an upper case letter, the message is
           "The lower case character correspond to <char> is ___. "
   3. If <char> is not a letter, the message is
           "<Char> is not a letter.                                                                      */




#include <iostream>


using namespace std;


int main()
{


  char letter;


  //prompt the user for letter




  cout << "Type in any letter:\n";
  cin  >> letter;
  cout << "\n";


  //print the appropriate message


  if (letter >= 65 && letter <=90) 
         cout << "The lower case character corresponds to '" << letter <<"' is " << (char)(letter + 32) <<".\n";


  else if (letter >= 97 && letter <=122) 
         cout << "The upper case character corresponds to '" << letter <<"' is " << (char)(letter - 32) << ".\n";


  else 
         cout << "The character '" << letter <<"' is not a letter.\n";


  system("pause");


  return 0;


}

Notice that I put

char letter;

However, the example answer given for the question number 3 @ C++ EXERCISES 2 is
this http://www.doc.ic.ac.uk/~wjk/C++Intr...illerEA2-3.cpp.

Can you please tell me why he/she alter the line to this??

char letter = 'a';

Thank you.

It is unnecessary since the first thing that you do to the variable is to read into it. It is typically good to initialise your variables, but in this case there is no real good default value to initialise it to. As such, to avoid using such a variable before reading into it, you should declare the variable as close as possible to the point where it is read into (or first used).

Thanks for the reply but sorry, I don't really understand your explanation. First, I think I need to know what 'initialize' mean. Can you please explain what 'initialize' mean?

Thank you.

initialize is to give your variable a sensible value before using it - for reasons which should be obvious - or will be if you think about it / encounter enough bugs.

From an english language dictionary

initialize, verb. To set variables, counters, or switches to their starting values.

regarding your 'is it neccesary' question, in the light of initialisation - picture a scenario where var letter is used to determine a menu choice - however in this menu program there is a default selection of 'a' - so if the user opens the program and chooses to start a process rather than going to the options menu, then process will begin with option 'a' as a run parameter telling the process which path of execution to take, waht the calculations are and what is output etc, -
if var letter was not initialised in this way in the scenario then what do you think might happen?

Correct me if I'm wrong.

From my understanding after take a few times reading your reply, here's what comes to surface of my understanding:

Say, here's the menu in a restaurant: dish A , dish B , dish C and dish D.

I set the initialization to dish C.

So, if the customer want to eat immediately without going through the menu, by default, the customer will have to eat dish C.

Am I right? =/

yes

in a restaurant offering a set 3 course 'plat du jour' but also does a la carte:

start program
initialise choice to c
message from program:
"Would you like to see the A la carte menu? Y/N"
user enters N
plat du jour (c) is served by default

I have a problem with rogsters' example, since the variable he initialized and the choice he makes don't seem to be related. If choosing a default option is rude/not possible then you must choose a starting value that is not valid and catch mistakes later on, or arrange the code in a fashion that makes initialization not required.

I agree it is a somewhat strained example - however - pedantry aside I was trying to think of something that illustrated the point wihtin the confines of the theme.

for the OP here is a perhaps more useful look at what i am getting at - it is a very basic skeleton only and as our friend whiteflags points out would require a lot more substance in terms of validation etc - but anyway, the idea of this example is for you to compile it once as is, and choose option n when prompted - then remove the initialision of char choice -recompile - and again choose option n - and then see waht your final output looks like.

Code:

#include <iostream>

void PrepareOrder(char choice)
{
    std::cout << "Chef leGranFromage is preparing your food now\n\n";

    if(choice == 'p')
    {
        std::cout << "your order was the plat du jour\n\n";
    }
    else
    {
        std::cout << "your order was option: " << choice << "\n\n";
    }
}

char GetAlaCarte()
{
    char poshOrder = 'Z';

    std::cout << "A La Carte Menu\n\n";
    std::cout << "(a) Badgers Snout dressed in a foam of dolphin's tears\n";
    std::cout << "(b) Sparrow with its legs tied toegether with a garnish of friacaseed snails\n";
    std::cout << "(c) Alphabet shapes with baked beans and chicken nuggets\n\n";

    std::cout << "Enter your order : ";
    std::cin >> poshOrder;
    std::cout << "\n\n";

    return poshOrder;

}

int main()
{
    char choice = 'p'; //init
    char seeMenu = 'Z'; //me too - so i know there is a known value in this variable

    std::cout << "Welcome to Big Time Charlie's Bistro\n\n";
    std::cout << "We assume you are going to eat the plat du jour but just in case you have more money..\n";
    std::cout << "Would you like to see the expensive a la carte menu?  y / n \n";
    std::cin >> seeMenu;
    std::cout << "\n\n";

    if(seeMenu == 'y')
    {
        choice = GetAlaCarte();
    }

    PrepareOrder(choice);


    return 0;
}

I think I understand what initial mean now.

rogster001's code was kind of a bit too complex for me though - is that some kind of code where you learn in your basic, or is that something you learn when you move into further chapter when learning C++?

This kind of worrying me because I don't have any teacher except being dependent on the internet as a source of learning C++.

Anyway, thank you. I now understand the basic concept of initials.

As long as you understand what I said the examples can be as complex as you like. Keeping with the menu theme, imagine there are functions to serve specific orders.

Here's an example that arranges the code in such a way that initialization is not an issue.

Code:

int choice = getChoice();
while (choice != QUIT_CHOICE) {
   if (choice == 1) {
      ServePizza();
   }
   else if (choice == 2) {
      ServeBurger();
   }
   ...
   else if (choice == X) {
      ServeX();
   }
   /*else {
      BadChoice();
   }*/
   choice = getChoice();
}

This code implies that getChoice() is a function that will only return valid choices. But suppose you did not have such a convenient function. Well, if input completely fails on the first try you have the protection of BadChoice(); when it is uncommented. After the first choice you can continue use BadChoice(); to protect yourself.