Conditional Statements

program Project1;

{$APPTYPE CONSOLE}

var
Answer : Char;

begin
	Write('Do you consider yourself a hot-tempered individual? ');
	Readln(Answer);

	Write(Chr(10), 'Press any key to continue...');
	Readln;
end. 

Do you consider yourself a hot-tempered individual? g

Press any key to continue...

Write('Do you consider yourself a hot-tempered individual(y=Yes/n=No)? ');

if a Condition is True

In Object Pascal, comparisons are made from statements. Examples of statements are:

• "You are 12 years old" 
• "It is raining outside" 
• "You live in Sydney"

One of the comparisons the computer performs is to find out if a statement is true (in reality, programmers (like you) write these statements and the computer only follows your logic). If a statement is true, the computer acts on a subsequent instruction.

The comparison using the if statement is used to check whether a condition is true or false. The syntax to use it is:

If the Condition is true, then the compiler would execute the Statement. The compiler ignores anything else:

If the statement to execute is (very) short, you can write it on the same line with the condition that is being checked. Consider a program that is asking a user to answer Yes or No to a question such as "Are you ready to provide your credit card number?". A source file of such a program could look like this:

This would produce:

You can write the if condition and the statement on different lines. This makes your program easier to read. The above code could be written as follows:

You can also write the statement on its own line if the statement is too long to fit on the same line with the condition. Although the (simple) if statement is used to check one condition, it can lead to executing multiple dependent statements. If that is the case, the statement section must start with the begin keyword and with the end keyword. Here is an example:

Here is an example of running the program:

If you omit the begin and end combination, only the statement that immediately follows the condition would be executed.

The if condition is used to check one possibility and ignore anything else. Usually, other conditions should be considered. In this case, you can use more than one if statement. For example, on a program that asks a user to answer Yes or No, although the positive answer is the most expected, it is important to offer an alternate statement in case the user provides another answer. Here is an example:

Here is an example of running the program:

The problem with the above program is that the second if is not an alternative to the first, it is just another condition that the program has to check and execute after executing the first. On that program, if the user provides y as the answer to the question, the compiler would execute the content of its statement and the compiler would execute the second if condition.

You can also ask the compiler to check a condition; if that condition is true, the compiler would execute the intended statement. Otherwise, the compiler would execute alternate statement. This is performed using the syntax:

The above program would better be written as:

Here is an example of running the program:

Notice that the Statement in the if condition does not end with a semi-colon. If the Statement of the if condition spans more than one line using the begin and end combination, the last line of its statement and its end keywords should not use a semi-colon but the lines above them must. Here is an example:

The if…else if and if…else if…else Statements

The previous conditional formula is used to execute one of two alternatives. Sometimes, your program will need to check many more than that. The syntax for such a situation is:

An alternative syntax would add the last else as follows:

if Condition1 then Statement1else if Condition2 then Statement2else Statement-n; if Condition1 then Statement1else if Condition2 then Statement2else if Condition3 then Statement3else Statement-n;

The compiler will check the first condition. If Condition1 is true, it will execute Statement1. If Condition1 is false, then the compiler will check the second condition. If Condition2 is true, it will execute Statement2. When the compiler finds a Condition-n to be true, it will execute its corresponding statement. It that Condition-n is false, the compiler will check the subsequent condition. This means you can include as many conditions as you see fit using the else if statement. If after examining all the known possible conditions you still think that there might be an unexpected condition, you can use the optional single else.

A program we previously wrote was considering that any answer other than y was negative. It would be more professional to consider a negative answer because the program anticipated one. Therefore, here is a better version of the program:

Here is an example of running the program:

The case...of Statement

When defining an expression whose result would lead to a specific program execution, the case...of statement considers that result and executes a statement based on the possible outcome of that expression. The different outcomes are listed in the body of the case...of statement and each case has its own execution, if necessary. The syntax of the case...of statement is:

The expression to examine can be an integer, a character, an enumeration type, or a predefined list of items. Here is an example of using the case…of statement:

Here is an example of running the program:

The program above would request a number from the user. If he types 1, it would execute the first statement. If the user types 2, it would execute the second statement, etc. If the user types any other number, no case would execute.

When establishing the possible outcomes that the case…of statement should consider, at times there will be other possibilities other than those listed and you will be likely to consider them. This special case is handled by the else keyword. The else case would be considered if none of the listed cases matches the supplied answer. The syntax of using the else condition and executing its statement is: 

Therefore another version of the program above would be

Here is an example of running the program: