Declaring constants in Pascal

A constant is a value that is given a name. The constant can be used anywhere in a program and will always have the same value.
Constants are declared in the declaration section of the program, that is the section before begin using the keyword, Const.
Value

Constant name Name: data type= value;

Data type

A command is an instruction that is a single word. Eg. READ
For example to declare a constant to store a value for tax:
Const Tax: real=.15;
TEST YOUR UNDERSTANDING
Initialize the following constants in Pascal: i. ii. The number of seconds in a minute. iii. The temperature at which water boils iv. The number of months in a year. v. The discount amount for 5%.

Writing data to the screen (WRITE and WRITELN)
Pascal uses write and writeln to display information on the computer screen. These statements are useful when prompting user for data and displaying information of a processed result to the screen.

* Writeln is also useful when a space is needed in the program. You can create a space by typing:
WRITELN;
* Writeln can also be used to display a string and a variable:
WRITELN (‘the sum is’, sum);
Before you read, you must write. The write is used when we want the data to be displayed on the same line, while writeln is used when we want to accept data in a new line. Place the information that you are writing to the screen in brackets and single quotes.
Example:
Write (‘enter your grade’); writeln (‘enter your grade’);
Read (G); Read (G);
Results
enter your grade 14 enter your grade 14
Reading data entered by the user (READ and READLN)
The READ statement and READLN statements are used to accept data that is input by the user. Take for example Read(G) takes the value entered by the user and stores it in the variable G.

The difference between Read and Readln is that when the data is accepted by read, it will stay on the same line, while Readln moves to the next line after accepting the data.

Readln should also be used to keep the data on the screen. If the readln statement is missing in the program, then output messages will be displayed on the screen without giving the user a chance to view. Therefore place READLN; before the END. statement.

TEST YOUR UNDERSTANDING
Write an algorithm to accept the name, age, height and amount paid the user. Print the information.
Rewrite it using Pascal syntax. After it is corrected, user your Pascal compiler to run the program.

PROCESSING INSTRUCTIONS
These instructions perform the calculations in a program. The symbol used for processing instructions is :=
For example A:=T + D

Depending on the data type of the values involved in a calculation, specific operator may be required as well as the result will be of a certain data type. The operators div and mod only work with integers.

Operator | Operation | Operands | Result | example | + | Addition | Real or integer | Real or integer | 2+3=5 | - | Subtraction | Real or integer | Real or integer | 10-8=2 | * | Multiplication | Real or integer | Real or integer | 2*3=6 | / | Real division | Real or integer | Real | 5.94/3.6=1.65 | Div | Integer division | Integer | Integer | 10 div 3=3 (the remainder is discarded) | mod | Modulus(remainder in a div operation | Integer | Integer | 10 mod 3=1 |

TEST YOUR UNDERSTANDING 1. Write a program to find the remainder R, when one integer A, is divided by another integer B. 2. Three integer variables are declared; num1, num2 and answer. Num1 is initialized to 20 while num2 to 5. Divide num1 by num2 and store the result in answer. 3. Write a program to accept three numbers and find the average. 4. A store is offering a 20% discount on all items. Accept the original price for the item and calculate the price after discount. 5. Write a program to compute the VAT payable on an item. The program should ask the user to enter price of an item and compute the VAT payable on the item using a fixed rate of 16% of the price. 6. There are seven errors in the program code below: correct them
Program TEST (output) ____________________________________
Var Number1, Number2; integer; ____________________________________
Begin; ____________________________________ Number1=24; ____________________________________ Number2:=Number1*4; ____________________________________ Writeln(‘help) ____________________________________
End ____________________________________

7. QUESTIONS 1. Identify the input and output statements between the BEGIN and END statements. 2. Identify the input statement between the BEGIN and END statements. 3. The total profit entered is $10,000, calculate omar, alvita and lov’a share of the profit.
PROGRAM profit_division;
VAR
total_profit : real; share_omar : real; share_alvita : real; share_lora: real;
BEGIN
{user enters the total profit} Writeln(‘enter the total profit’); Readln(total_profit); share_omar:= total_profit/2; writeln(‘omar receives$’, share_omar); share_alvita:= total_profit $*0.03; writeln(‘alvita receives $’, share_alvita); share_lora:= total_profit*0.02; writeln(‘lova receives $’, share_lora);
END.

8. A user enters letter a during the execution of a program, how would you describe that data? 9. What command would you use to create prompting statements in Pascal? 10. If a variable is declared called weight to store the weight of persons in centimetres, what would be the most suitable data type?

Special reserved word of the CRT unit
Pascal uses a number of functions that can enhance the presentation and perform special tasks. To include a library in a program, one should use the reserved word uses because it is used to call a library of functions and procedures.

The Cathode Ray Tube (CRT)library has a wide range of functions and procedures. Let us examine the functions below: Reserved Word | Description | Clrscr | Clears screen | Textcolor(word/int) | Color of text | Readkey | Reads a key; could be assigned to a variable |

Observe the following program

PROGRAM Sum;
Uses Crt; { The function is called using at the beginning of the programming in the declaration section.}
VAR
A, B, SUM: REAL;
BEGIN
Clrscr; {clears any information on the screen}
Textcolor(red);
Writeln (‘input two numbers’);
Writeln;
Readln (A, B);
Sum:= A+B;
Writeln (Sum);
Write(‘press any key to continue’);
Readkey; {program moves as soon as a key is pressed}
Readln;
END.

Lesson 9: Conditional Statements in Pascal
EXAMPLE
Program marks;
Var
m:integer; begin writeln(‘enter your marks’); read(m); If m>=50 then

writeln(‘you have passed the course’); end. To test a condition in a control structure, the relational operators that were taught in lesson 3 are used.

The IF-Then control structure
Syntax: if <condition> then <Statement>;

Notice that there is no End If at the end as we would have written in algorithm, only a semi-colon at the end of the last statement.

If we want to execute two or more statements if the condition is true, then we need to open a new begin and end statements to group the statements to be executed. The new begin and end act like brackets around the statements.

EXAMPLE
Program marks;
Var
m:integer;
Begin
writeln(‘enter your marks’); read(m); If m>=50 then
Begin
writeln(‘your mark is’, m ); writeln(‘you have passed the course’);
End;
End.

TEST YOUR UNDERSTANDING

1. Write a program to accept two values and interchange them if the first value is greater than the second. 2. A teacher wishes to assign comments for the student’s grades at the end of the term. If the grade is 80%, the output should be “you have done well!” write Pascal code to implement the program.

3. Write code to input a number. If it is 10, output its square.

4. Write code to input a grade. If this grade is greater than 100, output the message "TOO HIGH".

5. KFC decided to give a free coupon to persons whose order exceeds $1200.00. if the order is greater than $1200.00 then the computer will output “ Collect your free coupon”

6. A shop sells phone cards for $120.00 and reduces the amount a customer has to pay by subtracting $120.00 if the amount of phone cards bought for the week is ten or more. Read the phone cards bought and print the amount paid.

7. The IF-THEN-ELSE construct is one statement, hence use one semicolon
In a certain theatre where tickets normally cost 20 TL each. There is a 20% discount if one person buys more than 15 tickets. Input how many tickets a person has bought. Check if a discount is necessary and output the total amount he must pay.

The IF-then -Else statement
Syntax:

If <condition> then <statement1>
Else
<statement2>;

If <condition> then Begin <statement1>; <statement2>; End
Else
Begin <statement3>; <statement4>; End;

Please note that there is no semicolon after the word End If, if it is followed by an else.

TEST YOUR UNDERSTANDING

1. A bonus of $150.00 is given to employees who were absent for less than 4 days in a year. The bonus is added to the salary to arrive at the total income. If the total income is greater than $300.00, a tax of 5% is deducted. Input the days absent and the salary. Output the total income, the tax deducted and the income less tax. 2. Input a number. If it is less than 10, output its square. If it is more than 10, output the number only. 3. A technician charges fees based on the number of hours worked as follows: * Two hours or less, a fee of $90.00 per hour * Up to six hours, a fee of $75.00 per hour * More than six hours, a fee of $60.00 per hour
Write Pascal code to input the hours worked. The algorithm should output the hours worked and the fees charged.

4. Input a student's ID number and final grade. Print the student's ID with a message telling him whether he passed or failed according to his grade. If the final grade is greater or equal to 50 he passed, if the final grade is less than 50 he failed.

Boolean operators (AND or OR)

Boolean syntax:

IF(<condition1> )AND(<condition2>) THEN
IF (<condition1> )OR (<condition2>) THEN
TEST YOUR UNDERSTANDING

1. Write Pascal code to read the name of the student and the value of the student’s mark. Print the name of the student and the appropriate grade based on the following grading scheme:
80 or more A
Less than 80 but more than or equal to 65 B
Less than 65 but more than or equal to 50 C
Less than 50 but more than or equal to 35 D
Less than 35 F 2. A company gives out bonuses based on the amount of income generated by the sale representative. Once the income is greater than $5000.00, and less than or equal to $8000 then bonus of 10% of the generated income is payable, otherwise the bonus is 3% of the income generated. Read the income generated and print the bonus.

Lesson 9: Writing loops in Pascal

Repitition control structures (loops)

The While-do loop The Repeat-until loop The For-Loop
Syntax: syntax: syntax:
While <condition> do Repeat For <loop counter>:=<range> do <statement>; <statement>; <statement>; Until <condition>;

Please note that new begin and end statements for more than one statement also applies for loops!

For 1. Write Pascal code to display the name and age of fifty students in a class. 2. Amanda is a fitness consultant and charges $10 per hour with clients. Write Pascal code that takes in the number of hours she worked per day and calculates how much she has earned after 7 days. 3. Create a four times multiplication table for the numbers 1 to 6 4. Calculate the sum of all odd numbers between 1 and 20. Print the total. 5. Write Pascal code that takes in the ages of 25 people and find the youngest. 6. Write Pascal code to enter 10 numbers and find the highest and lowest exclusively

While 1. Find the largest of a series of integers terminated by 0. 2. Write Pascal code to enter the marks of students terminated by 999 3. Find the average of three numbers. Accept these three numbers and calculate the average until the user enters “no” to stop the program. Print the average.

Repeat until 1. Write Pascal code to input a set of numbers until number is equal to 0 reached. Find the highest and lowest of each number input by the user then print the highest and lowest.

Lesson 9: ARRAYS
There are times where you might have to store a list of items for one variable, for storing so many values to one variable you can use an array.
An array is made up of elements each of which acts like a separate variable. Every element in the array has the same name, but is distinguished from each other by a subscript or index, which is a number placed in brackets. All the elements in an array must have the same data type.
If the array called LETTERS is represented like this: Element | F | R | I | S | U | T | Subscript/ index | 1 | 2 | 3 | 4 | 5 | 6 |

The second tow contains all the subscripts or index. All subscripts are arranged in order and usually starts from one or zero (1/0).
The first row stores the contents of each subscript. It is known as the array element. These are arranged in the order in which the information was assigned or in the order that the user entered the data. Therefore the elements are in no specific order.
Declaring Arrays
When declaring an array, you specify the name, size and data type of the array. Please note that all elements in an array must have the same data type and are declared in the declaration section of the program.
Syntax: VAR ArrayName: ARRAY[1….number_of_elements] of data_ type;
Let us declare the array named LETTERS with in the above example:
PROGRAM ARR;
VAR
LETTERS : ARRAY[1..6]of CHAR;

TEST YOUR UNDERSTANDING
The following represents an array called SCORES: 45 | 78 | 90 | 35 | 78 | 90 | 34 | 12 | 56 | 89 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 1. Which of the rows has the subscripts? 2. Which row shows the elements? 3. What value is stored in index 7? 4. Declare the array
Declare each of the following:
Variable name data type Arraysize
NUMBER real 25
Studentname string 18

Manipulating an array
To manually store a value to an element in an array we follow the method:
<array_name>[subscript]:= value;
The procedure for storing the value D in the third element of the array LETTERS is: LETTERS [3]:=’D’;

You can also use an array to element to assign a value to assign a value to variable. For example
L := LETTER[4];
TEST YOUR UNDERSTANDING
Store the following values to the arrays declared above * 50 and 67 to the second and fifth element in SCORE. * Tom and Susan to the first and tenth element in Studentname. * 1000 to the 9th index in the NUMBER array.

Reading and Writing to an array * Elements can be read to and written from each subscript of an array manually.

lines
1 PROGRAM read_array;
2 VAR
3 num: Array[1..5] of integer;
4 BEGIN
5 num [2]:=25;
6 writeln (num [2]);
7 Write (‘input a number’);
8 Read (num[5];
9 Write (num[5]);
10 END.

Lines 1-3 is the block of the program where an array called num with 5 elements is being declared in line 3. The Execution of the program starts after the begin instruction. In line 5 the value 25 is being assigned to the second index of the array. In line 6, we use the write command to output the content of subscript 5.

In line 7, a prompt is printed to the user to enter a number. This number is read to the fifth index of the array. Line 9 will print the content of num[5].

* Arrays can also be used to perform calculations. Consider the following calculation:
Program cal_array;
Var
Grades1: array [1...6] of real; Grades2: array [1...6] of real; Ans: real;
BEGIN
Grade1[1]:5; Grade2[1]:17; Ans:= Grade2[1]:17- Grade1[1]:5; Write(Ans)
End.

TEST YOUR UNDERSTANDING 1. Write a program in Pascal that declares an array called NAMES. The array should have 10 elements and should assign Sam and Joy as the fifth and tenth elements. Print these elements. 2. Write a program in Pascal that declares an array called int_num. The array should have 16 elements and should assign accept three values from the keyboard to be entered into its 4th, 6th and 8th element. Print these elements.

3. Consider the code below.
Program Addition;
Var
A: Array[1...2] of integer; B: Array[1...2] of integer; S: Array[1...2] of integer; Sum: integer;
Begin
Writeln (‘input a number’); Read(A[1]); Writeln; Writeln (‘input a second number’); Read (A[2]); Writeln (‘input a third number’); Read (B[1]); Writeln; Writeln (‘input a third number’); Read (2[1]); Writeln; S[1]:= A[1]+B[1]; S[2]:= A[2]+B[2]; Sum:= S[1] + S[2]; Writeln(‘the sum of both arrays are’, Sum); Readln;
End.

1. State the name of the program 2. State the name of the Array/s. 3. What is the size of A? 4. In the line, Read(A[1]); what is the program doing? 5. What is the purpose of the single writeln? 6. If inputs to the program are 10, 2, 3, 5, what would be the sum at the end of the program? 7. State the purpose of the readln that falls before the end.

Traversing an Array
In the above question, what if the array size was 1000, this therefore means that when assigning values, we would need to request the values 1000 times then read them 1000 times then find 1000 some. This would however be burdensome to write. The array can be traversed that is using the For-loop to assign values to each element one at a time.

Consider the following example that will accept and the scores of 1000 students:
Program Loop;
Var
ArScore: array [1...1000] of integer; X: integer;
Begin
For X:= 1 to 1000 do Writeln (‘enter the student score’); Read (ArScore[X]); Writeln (ArScore[X]); Readln; End.

TEST YOUR UNDERSTANDING 1. Write code fragment to do the following: * Declare an array of 15 integers named img. * store 31 in the 10th element of array img. * Use a for loop to store values in each element. The program should request the amount paid of the fifteen persons and assign it to each element.

2. Consider the following program in Pascal and answer the questions that follow: 2010 Q 12
Program HUM (input, output);
VAR CSEC: array[1..8] of integer; Start, inc: integer;
Begin
Inc:=0; For Start: 1 to 8 DO CSEC[start]:=Inc;
End.

a. State the name of the program b. State the name of the array c. State the size of the array d. Explain the purpose of the array 3. The following shows the records of the miles that students walked in a marathon Students | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | miles | 34 | 12 | 2 | 34 | 61 | 32 | 12 | 12 | 45 | a. Which row contains the elements of the array? b. Write code to change the value for student 3 to 32. c. Write a program in Pascal to declare the array. d. Write code to display all the contents of the array.

Searching an Array
An array can be searched by using the for loop to compare each value until the desired result is found. This is called a linear search. Consider the Pascal code below that searches the elements of the array for the value 90:
Program search;
Var
ArScore: array [1...1000] of integer; X: integer;
Begin
For X:= 1 to 1000 do Writeln (‘enter the student score’); Read (ArScore[X]); If ArScore[X]:=90 then Writeln (ArScore[X]) Else Write (‘score not found’); Readln; End.

TEST YOUR UNDERSTANDING

1. A Pascal program contains 10 integers in an array named LONG. Write codes to print the sum of all the integers and find all integers smaller than the integer nine (9). 2011 Q 10