Class Notes of Data Structures
Dr. David B. Y. Tsai Feb., 2009
IM-2B
Part Two
Preliminaries of Algorithmic Notation
Variable Names –
1. Using capital letters, as in MAX or Data. Single-letter names of variables used as
counters or subscripts will also be capitalized.
2. Variable Declaration: TYPE Variable, such as integer MAX
3. Local and Global Variables:
(1) A computer program may contain a main program and various subprograms has led to the
notation of local variables and Global variables.
(2) A subprogram contains its own list of variables, call local variables.
(3) Subprograms may contain parameters, variables which transfer data between a
subprogram and its calling program.
Assignment Statement –
Using dots-equal notation. Max := DATA[1]
Input and Output –
1.
2.
Using a Read statement to input and assign data to variables, such as Read :
Variable names.
Data in variables is output by using Write or Print statement with the form: Write:
Messages and/or variable names.
Procedures –
They will be used for an independent algorithmic module which solves a particular
problem.
Call SWITCH(DataA, DataB)
:
Procedure: SWITCH (DA, DB)
1. Set TEMP:= DA, DA:=DB and DB:= TEMP.
2. Return.
Control Structures
1. Sequential flow
2. Conditional flow – [End of If structure]
(1) Single alternative
If condition, then:
[Module A]
[End of If structure.]
(2) Double alternative
If condition, then:
[Module A]
Else:
[Module B]
[End of If structure.]
(3) Multiple alternative
If condition(1), then:
[Module A1]
Class Notes of Data Structures
Dr. David B. Y. Tsai Feb., 2009
IM-2B
Else If condition(1), then:
[Module A2]
:
Else If condition(M), then:
[Module AM]
Else:
[Module B]
[End of If structure.]
3. Repetitive flow
Repeat for K = R to S by T:
[Module]
[End of loop.]
Repeat while condition:
[Module]
[End of loop.]
EXAMPLE:
Algorithm: to find the location LOC and the value MAX of the largest element of DATA.
1. Set K:=1, LOC:=1 and MAX:=DATA[1]
2. Repeat Step 3 and 4 while K ≦ N:
3.
If MAX ＜ DATA[k], then:
Set LOC:=K and MAX:=DATA[k].
[End of If Struture.]
4.
Set K:=K+1.
[End of Step 2 loop.]
5. Write: LOC, MAX.
6. Exit.
Space Allocation
1. Space requirement
P := new(space size) [pointer variable P]
Example:
integer *P [to declare a pointer variable P]
P:= new(integer) [to allocate an integer space whose address is stored into P variable]
*P:=10 [variable P point a space which contains data 10]
2. Space release
delete(p)
[variable p contains the beginning address of space to be deleted]