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 structureIt 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 matchelse 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