Basic operations
The assignment
We use the assignment operator to store a value in a variable.
Syntax
variable_name := expression;
Arithmetic operations
The arithmetic operators in Pascal are:
Operator
+
-
*
/
div
mod
Operation
Addition or unary positive
Subtraction or unary negative
Multiplication
Real division
Integer division
Modulus (remainder in integer division)
Operands can be numeric values or variables.
The result of an operation is always assigned to a variable.
Example
program example;
var
radius, area : real;
begin
radius := 2;
area := 3.14 * radius * radius;
write(area);
end.
Example
program example;
var
dividend, divisor, quotient, remainder : integer;
begin
dividend := 12;
divisor := 7;
quotient := dividend div divisor;
remainder := dividend mod divisor;
writeln(quotient);
writeln(remainder);
end.
Boolean operators
The boolean operators in Pascal are:
Operator
not
and
or
xor
Operation
negation (~)
conjunction (∧)
disjunction (∨)
exclusive-or (⊻)
Example
program example;
var
n : integer;
b, c, d : boolean;
begin
n := 12;
b := (n mod 2) = 0;
writeln(n, ' is even?');
writeln(b);
c := (n mod 3) = 0;
writeln(n, ' is multiple of 3?');
writeln(c);
d := b and c;
writeln(n, ' is even and multiple of 3?');
writeln(d);
end.
Operations on a character
The character set includes letters, digits, spaces, punctuation marks, etc.
We use a code to encode the characters.
Unicode UTF-8 is the modern standard encoding.
Example
Character
Unicode
A
65
B
66
Z
90
a
97
b
98
Operations on a character in Pascal are:
ord(c)
chr(a)
succ(c)
pred(c)
order number in the code.
the result is the character whose code is the integer a.
successor of the character c in the code order.
predecessor of the character c in the code order.
Example
program example;
var
n : integer;
c, p, s : char;
begin
c := 'M';
n := ord(c);
writeln(n);
p := pred(c);
writeln(p);
s := succ(c);
writeln(s);
end.
Reading and writing data
In order to allow dialogue between the program and the user, the programming language includes instructions to read data entered on the keyboard, and instructions to display data on the screen.
Syntax
read(variable_name);
readln(variable_name);
write(variable_name);
writeln(variable_name);
writeln displays data and returns to the line.
Writing an integer number
The writing format of a value specifies the number of characters used to display that value.
Syntax
write(value : field_width);
The output is right-justified in a field of the specified integer width.
Example
Instruction
m := 123
write(m : 5)
write(m : 2)
Display
...
^^123 (^ is the space symbol)
123
Writing a real number
write(real_value)
displays a real number in scientific notation n.nnE+n preceded by a space.
write(real_value : field_width)
displays a real number in scientific notation in a field of the specified integer width.
write(real_value : field_width : decimals_width)
displays a real number in a field of the specified integer width and with the specified decimal width.
Example
Instruction
r := 123.456
write(r)
write(r : 8)
write(r : 8 : 2)
Display
...
^1.23456E+2
^1.23E+2
^^123.45
Example
Write a program that reads the value of the radius of a sphere, then calculates and displays the value of its volume.
The formula for the volume v of a sphere with a radius r is:
program sphere;
const
pi = 3.14;
var
radius, volume : real;
begin
writeln('enter radius:');
readln(radius);
volume := (4 / 3) * pi * radius * radius * radius;
writeln('volume: ', volume : 8 : 2);
end.