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Pascal Programming 101 (Variables (Integer (-32768 to + 32767), Real (e.g.…
Pascal Programming 101
Variables
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Char (e.g. 'A', '3', '!')
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Boolean (e.g. TRUE, FALSE)
Functions
Mathematical
sqr(X), square, sqr(2.5) gives 6.25
sqrt(X), square root, sqrt(4) gives 2
abs(X), absolute value, abs(-3) gives 3
int(X), integer, int(5.67) gives 5.0
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Ordinal
odd(X), test for odd number, odd(3) gives TRUE
odd(4) gives FALSE
Transfer
chr(X), return char with ASCII value X, chr(65) gives 'A'
ord('X'), return ASCII value of char 'X', ord('A') gives 65
round(X), round(4.56) gives 5
trunc(X), trunc(4.56) gives 4
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User-defined function
function cube(N : integer) : real;
begin
cube := N＊N＊N
end;
begin { main program }
writeln( cube(2) )
end.
output: 8.0
Strings
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Functions
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concat, +
'a' + 'b' + 'c' gives 'abc'
'X' + 'YZ' gives 'XYZ'
concat('X', 'YZ') gives 'XYZ'
copy
Format: copy(string, start position, number of copy chars)
copy('TRUE LIGHT', 1, 4) gives 'TRUE'
copy('TRUE LIGHT', 6, 5) gives 'LIGHT'
pos
Search for position of a char in a string
pos('E', 'TRUE LIGHT) gives 4
pos('A', 'TRUE LIGHT') gives 0
Procedures
STR
STR(123, strg);
stores '123' to strg
STR(3.1416 :4:2, strg);
stores 3.14 to strg
VAL
VAL('123', num, errorpos);
stores 123 to num, errorpos = 0 (because no error occurs)
VAL('123abc', num, errorpos);
stores 0 to num, errorpos = 4 (because error occurs at 4th char)
String as Array of characters
if S = 'TRUE LIGHT', then
S[1] = 'T'
S[4] = 'E'
S[5] = ' '
for count := 1 to length(S) do
write( S[count] );
output: TRUE LIGHT
Arrays
Declaration
mark : array[1..10] of integer;
grade : array[1..20] of char;
gradecount : array['A' ..'E'] of integer;
var score : array[1..40] of integer;
max := score[1];
min := score[1];
for count := 2 to 40 do
if score[count] > max then max := score[count];
if score[count] < min then min := score[count];
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Searching an array
var name : array[1..40] of string;
found := false;
target := 'CHAN SIU LING';
for count := 1 to 40 do
if target = name[count] then found := true;
if found then writeln('name found!');
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2D array
Declaration
var X : array[1..2, 1..3] of char;
X[1, 2] \( \neq \) X[2, 1]
Tabular output
for row := 1 to 2 do
begin
for col := 1 to 3 do
write(X[row, col])
writeln;
end;
Tabular input
for row := 1 to 2 do
begin
for col := 1 to 3 do
read(X[row, col])
readln;
end;
Operators
Arithmetic
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div, 9 div 2 gives 4 (quotient)
mod, 9 mod 2 gives 1 (remainder)
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Procedures
Declaration
Must be declared before main program
procedure <title>;
var <variables>;
begin
<statement>
end;
Variables
Global variable
program test2;
var X : integer; { global var }
procedure addone;
begin
X := X + 1;
end;
begin { main program }
X := 10;
addone;
writeln(X)
end.
output: 11
Local variable
program test1;
var X, Y : integer; { global var }
procedure swap;
var temp : integer; { local var }
begin
temp := X;
X := Y;
Y := temp
end;
begin { main program }
X := 1; Y := 2;
swap;
writeln(X, Y)
end.
output: 21
Parameters
Using parameters make procedures more standalone, more modular
program test3;
var X : integer;
procedure addone(Y : integer);
begin
Y := Y + 1;
end;
begin { main program }
X := 10;
addone(X);
writeln(X)
end.
output: 10
program test4;
var X : integer;
procedure addone(var Y : integer);
begin
Y := Y + 1;
end;
begin { main program }
X := 10;
addone(X);
writeln(X)
end.
output: 11
Advantages
- Breaking long programs into smaller manageable parts called modules, easier to write, test, debug, maintain
- More efficient program development
- Procedures/sub programs can be re-used
- Facilitate division of labour in a coding team, large projects can be developed in parallel
Basic statement
Assignment statement A := 1;
Assignment operator :=
Variable A is like a box in computer memory
Input statements
readln(X);
read(X);
Input value from keyboard and store in variable X
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Selection statement
if statement
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Nested if statement
if <condition 1>
then if <condition 2>
then <statement 1>
else <statement 2>
else if <condition 3>
then <statement 3>
else <statement 4>;
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