In C#, we declare variables according to their types, such as number type, text type, and so on.

We determined that "int a;" will be an integer type for the variable named 'a'.
We determined that "string b;" will be a string type for the variable named 'b'.
We defined that "double c;" will be a decimal number for the variable named 'c'.

Assignment of values to these variables can be done at any step of the program:
a=10;
b="Cryptograph";
c=5.5;

Variables are used for entering values from the outside, comparing these values, putting them into a loop, and doing other tasks. Any value can be entered from the outside, so it is a variable. To read a value entered from the outside, we use the Console.ReadLine() command. If we want to read a string type variable, we use b=Console.ReadLine();. But if we are going to read a number type variable, we should use a conversion function because the Console.ReadLine command reads as a string. a=Convert.ToInt32(Console.ReadLine()); this way, we read an int type variable, c = Convert.ToDouble(Console.ReadLine()); and with this command, we read a double type variable.

If-Else structure
It is used to compare a value entered from the outside or a value coming from a different source.
if (value to be compared) action to be taken in case of a match
else action to be taken if the comparison does not match

a=Convert.ToInt32(Console.ReadLine());
if(a==5) Console.WriteLine("Niyazi Alpay");
else Console.WriteLine("Wrong Number");

If the variable 'a' comes as 5, print Niyazi Alpay to the screen; otherwise, print Wrong Number.
If we want to perform multiple operations when the condition is met, we do it within {} parentheses.

a=Convert.ToInt32(Console.ReadLine());
if(a==5){
 Console.WriteLine("Niyazi Alpay");
 Console.WriteLine("Muhammad");
}
else Console.WriteLine("Wrong Number");

We can also perform multiple comparisons.

a=Convert.ToInt32(Console.ReadLine());
if(a==5){
 Console.WriteLine("Niyazi Alpay");
 Console.WriteLine("Muhammad");
}
else if(a==10) Console.WriteLine("Cryptograph");
else Console.WriteLine("Wrong Number");

The arithmetic characters we use when comparing are:
== if equal
> if greater
< if less
>= if greater than or equal to
<= if less than or equal to
=== if strictly equal