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Learning C: lesson 2

Hello, this is Alexander. Since I finally got an email from someone who liked my previous
lesson, I am going to make the second installment. This one will be about variables, and
stuff like 'if' statements.


'IF' is the most important word in programming for many programs. Without it there is no
conditional statements. This means that there can be only one way a program can execute.
It would almost impossible to make a program without this one simple word.


There are many things to understand when using IF statements. First, you must understand
stuff like OR NOT etc. This are the most important, so I will describe how to use them in
C and C++ programming below: (NOTE: ZERO IS FALSE! ONE IS TRUE!)


NOT: This just says that the program should reverse the value...for example NOT(1) would be
0. NOT(0) would be 1. NOT(any number but zero) would be 0. In C and C++ NOT is written
as - ! - just one simple little character. It is very useful and can save lots of time.



AND: This is another important command, and it is used to say that if this AND this is
true... for example (1)AND(0) would come out as 0. (1)AND(1) would come out as 1. (ANY
REAL NUMBER BUT ZERO)AND(0) would be 0. (ANY REAL NUMBER BUT ZERO)AND(ANY REAL NUMBER BUT
ZERO) would be 1. The AND is written as - && - in C++. It is just two simple characters.


OR: Very useful is the OR statement! For example (1)OR(0) would be 1! (0)OR(0) would be
0. (ANY REAL NUMBER)OR(ANY REAL NUMBER BUT ZERO) would be 1! It is simple, either one can
be true and make the whole thing true. The OR is written as - || - in C++. It is also two
simple characters.



The next thing to learn is to combine them... What is !(1 && 0)? Of course, it would be
1. This is because 1 && 0 evaluates two 0 and ! 0 equals 1.


Try some of these...they are not hard. If you have questions about them, you can email me
at lallain@concentric.net.



A. !(1 || 0) ANSWER: 0
B. !(1 || 1 && 0) ANSWER: 0 (AND is evaluated before OR)
C. !((1 || 0) && 0) ANSWER: 1 (Parenthesis are useful)



If you find you enjoy this you might want to look more at Boolean Algebra, which is also
very helpful to programmers as it can be good for helping program conditional statements.



IF is used like this IF(TRUE)
{ DO WHAT IS IN THE BRACKETS }


ELSE is basically ELSE
{ DO WHAT IS IN THE BRACKETS }


Let's look at a simple program for you to try out on your own...



#include <iostream.h> //For output
#include <conio.h> //For getch()

void main() //Most important part of the program!
{
int age; //Need a variable...
cout<<"Please input your age: "; //Asks for age
cin>>age; //The input is put in age
if(age<100) //If the age is less than 100
{
cout<<"You are pretty young!"; //Just to show you the output
}
if(age==100) //Remember, if the age equals 100 needs two =
{
cout<<"You are old"; //Just to show you it works...
}
if(age>100)
{
cout<<"You are really old"; //Proof that it works for all conditions
}
}



Now, this program did not use && || ! or anything in it. This is because it didn't need
too. I think you should probably be able to make your own if statements with them without
having to worry too much about problems.