ICT aka Teknologi Maklumat & Komunikasi: Lesson 12 : Control Structures

Control structure is a structure of statements in programming that allows

the programmer to control the flow of a program.

Control structure can be divided into sequence, selection and repetition control structures.

SEQUENCE CONTROL

Sequence control refers to the linear execution of codes within a program. In sequence control, the statements are executed one by one in consecutive order.

In sequence control, the statements are executed one by one in consecutive order.

Lets see an example of pseudo code that has sequence control structure.

This program will request the user’s date of birth and then request today’s date, calculate the age and finally will print the user’s age.

For example, today’s date is 1-JAN-2006, then the results will be shown as follows:

Let’s see another example of pseudo code that has sequence control structure.

The following is the result of the example.

Lets see the flow chart for a general sequence control structure.

As we can see, the flow chart for sequence control is very simple.

It will execute statement 1 followed by statement 2 and any following statements.

EXAMPLE

The flow chart represents a program that will request the user’s date of birth and then request today’s date, calculate the age and finally will display the user’s age.

SELECTION CONTROL

There are times when you want your program to make a decision based on the situation given.

For example, a program that stores student’s marks may respond differently to different marks.

Or maybe a simple mathematical program will display its result as odd or even, based on the result.

Selection control enables the programmer to assign different events for different situations.

An example of selection control is “If...Then...Else” statement. The basic pseudo code for “If...Then...Else” statement is as follows.

Let's see a pseudo code example for the “If...Then...Else" statement for a program that will print “You are too heavy to ride the toy car” if the student’s weight is more than or equal to 50.

Otherwise it will print “You can ride the toy car”

Let's see the flow chart for a similar selection control example.

Let's see a program that will respond differently for different service hours in a school library.

A student requests her service hours in a library from the program, the

program will then check whether her service hours are more than/equal to 30 or not.

If the service hours are over or equal to 30, the program will print a message, “Thank you for your service”.

If the service hours are lower than 30 then the program will print a message, “Please continue to serve in the library”.

Let's write an example of a program that implements sequence control structure.

This program will declare a constant pi equal to 3.142. Then the program declares two variables to be used in the program (r and volume).

The program will then assign some value to the r variable.

The program will then calculate the volume using the formula volume = (4/3)πr

The program will then display the volume calculated with a message box.

Now write an example program that implements selection control structure.

Write a program that will retrieve the current date from the system.

If today’s date is more than 15 then the program will display a message box with the message “We are towards the end of the month”.

Else the program will print “We are at the beginning of the month”.

DIFFERENTIATE BETWEEN SELECTION CONTROL AND SEQUENCE CONTROL

EXT : REPETITION CONTROL STRUCTURES

Let’s learn about the last control structure which is repetition control structure. A repetition control structure allows the programmer to specify an

action to be repeated while some condition remains true.