TP3/Resources/TPLESSN1/TL09.TXT

TURBO-LESSONS - A Pascal Tutorial        Version 1.01    Page 36


TURBO-LESSON 9: FOR STATEMENT

OBJECTIVES - In lesson 9, you will learn about:

1.  Using ":n" to specify field width in Write statements
2.  FOR statement


1.  Using ":n" to specify field width in Write statements.

Spacing of output in previous lessons has been done using spaces 
in string constants, such as, 'I= '.  The space after the = will 
be printed as part of the string.

There is another way to add spaces.  When listing the items to 
write in a Write or WriteLn statement, ":n" can be added to 
specify how many characters the item is to occupy in the output.

For example:

WriteLn(I:4);

The value of I would be printed in a space 4 characters wide.

##### DO:

Run Program TEST1 several times with the following statements in 
the main part of the program: 

ReadLn(I);
WriteLn('[', I:4, ']');

Look closely at the output.  Are the numbers "left-justified" or 
"right-justified"?  

If I has a value of 23, and 23 prints in columns 1 and 2 of the 
4 column field, it is left-justified.  If the 23 appears in 
columns 3 and 4 of the 4 colunm field, it is right-justified.  

What happens if you enter a number that is too large to fit the 
field specified?

##### DO:

Run the program several times using the following values for I:

123,   1234,   -1234,   12345
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TURBO-LESSONS - A Pascal Tutorial        Version 1.01    Page 37 


2.  FOR statement.

In the previous lesson, you were reminded of the various ways to 
control the sequencing of program actions.  One of the REPETITION
structures is the FOR statement.  The forms of the statement are:

FOR variable := lowvalue TO highvalue DO
     Statement;   {May be a block statement with BEGIN END}

FOR variable := highvalue DOWNTO lowvalue DO
     Statement;

##### DO:

Run PROG9 several times to see how it works.

Experiment with both positive and negative numbers.

What happens if High is smaller than Low?

##### DO:

Run PROG9 using 5 for the Low, 3 for the High?

What was the result?

Also try 5 for both values.  How many times is the loop repeated 
if Low = High?

What results would you expect if you entered 3.4 for Low and 5.3 
for High?

##### DO:

Run the program with the values 3.4 and 5.3.

Were you correct in predicting the outcome?

Can constants be used instead the variables Low and High?

##### DO:

Edit the FOR statement in PROG9 as follows:

FOR Index := 1 to 5 DO

Run the Program.  

Is it possible to use expressions for Low and High?

##### DO:

Change the FOR statement to:

FOR Index := Low + 1 TO High DO

Run the Program.  
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