8 Subroutines, File Handling and Design

Question 1

What is a structure diagram?

Answer 1

• A modelling tool used to show the hierarchy of a system/program
• A graphical representation of top down design to show how a system is broken into subsystems
• They are used at the design stage of the software development lifecycle

Question 2

What are library routines?

Answer 2

A collection of standard programs/subroutines available for immediate use

Question 3

What is a subroutine?

Answer 3

• A self-contained piece of code that that is given a name and can called from within a program
• 2 types of subroutines
  
  • A function - always returns a value
  • A procedure - may or may not return a value

Question 4

What is a procedure?

Answer 4

A subroutine that does not have to return a value

Question 5

What is a function?

Answer 5

A subroutine that always returns a value

Question 6

Describe the use of a subroutine in a program

Answer 6

• It is a block of code within a program that can be called when needed
• It breaks up the program to make it easier to read and understand
• It can be reused by another program

Question 7

What is a library routine?

Answer 7

• A standard subroutine that is available for immediate use
• It can be called from many programs
• It is used often and makes programs easier/faster to write as the code is already written
• They make testing easier as they have already been used and debugged

Question 8

What is top down design?

Answer 8

Breaks down a system into successively smaller pieces/sub systems

Question 9

What are the benefits of top down design?

Answer 9

• allows several programmers to work at the same time on the software
• Development time is faster
• can test each subsystem independently
• Easier to debug

Question 10

What are the advantages of using library routines?

Answer 10

• Makes writing programs faster as we are reusing code
• Makes testing easier as the code has already been tested.

Question 11

The library routine DIV is used for integer division. What would the code below output?

i ← DIV(11, 4)
OUTPUT i

i ← DIV(3, 2)
OUTPUT i

i ← DIV(2, 4)

OUTPUT i

Answer 11

2

1

0

Question 12

The library routine MOD is used to find the remainder. What would the code below output?

i ← MOD(11, 4)
OUTPUT i

i ← MOD(3, 2)
OUTPUT i

i ← MOD(2, 4)

OUTPUT i

Answer 12

3

1

2

Question 13

The library routine ROUND is used to round a decimal number to a certain number of places. What would the code below output?

r ← ROUND(2.6789, 3)
OUTPUT r

r ← ROUND(3.142, 0)
OUTPUT r

r ← ROUND(1.111111, 4)
OUTPUT r

r ← ROUND(1.227, 2)
OUTPUT r

Answer 13

2.679
3
1.1111
1.23

Question 14

The library routine RANDOM returns a random number between 0 and 1 inclusive. What is the smallest and largest random number that could be generated by the pseudocode statement below.

value ← ROUND(RANDOM() * 100, 0)

Answer 14

Smallest = 0

Largest = 100

Question 15

The string handling library routine LENGTH returns the number of characters in a string. What would the call below return?

length = LENGTH(“Happy Days”)

Answer 15

10

Question 16

The string handling library routine LCASE returns the string with all characters in lower case.. What would the call below return?

word = LCASE(“LovEly”)

Answer 16

lovely

Question 17

The string handling library routine UCASE returns the string with all characters in upper case.. What would the call below return?

word = UCASE(“LovEly”)

Answer 17

LOVELY

Question 18

2The string handling library routine SUBSTRING returns a substring of a specified length starting at the position specified.

What would the calls below return?

s1 = SUBSTRING(“Happy Days”, 1, 5)

s2 = SUBSTRING(“Happy Days”, 2, 2)

Answer 18

s1 = “Happy”

s2 = “ap”

Question 19

What are the advantage of subroutines?

Answer 19

• Can sometimes be reused in other programs
• Breaks down code and makes it easier to read and debug
• Can be called many times, so code is not repeated

Question 20

What are parameters in a subroutine?

Answer 20

The variables in a procedure or function declaration that store the values passed from the main program to a procedure or function

Question 21

Write a procedure that accepts an integer as a parameter and a string. It should then output that string that number of times

Answer 21

PROCEDURE OutputSentence(numTimes: INTEGER, sentence: STRING)
    FOR int i ← 1 TO numTimes STEP 1
        OUTPUT sentence
    ENDFOR
ENDPROCEDURE

Question 22

Write a function that when given a radius (REAL) calculates and returns the area of a circle.

Answer 22

FUNCTION CalcCircleArea(radius: REAL) RETURNS REAL 
    REAL area \<- 0 
    area \<- 3.14159 \* radius \* radius 
    RETURN area 
ENDFUNCTION

Question 23

What are the 4 main stages of the Software Development Lifecycle

Answer 23

Analysis

Design

Coding

Testing

Question 24

Describe analysis in terms of the software development lifecycle

Answer 24

• Identification of the problem and the requirements specification (what a program is required to do)
• Involves abstraction and decomposition of the problem to identify exactly what is required.

Question 25

Describe design in terms of the software development lifecycle

Answer 25

* Uses the requirements specification from the analysis stage to show to how the program should be developed. * This can be formally documented using structure charts, flowcharts and pseudocode.

Question 26

Describe coding in terms of the software development lifecycle

Answer 26

* The program or set of programs are developed. * Each module of the program is written using a suitable programming language and then tested. * Iterative testing is conducted on modules and and code amended until the module performs as expected,

Question 27

Describe testing in terms of the software development lifecycle

Answer 27

* Systematic checks are done on a program to make sure that it works under all conditions. * The completed program is run many times with different sets of test data.

Question 28

What is abstraction?

Answer 28

The key elements required for a solution to the problem are kept and any unnecessary details and information that are not required are discarded

Question 29

What is decomposition?

Answer 29

A complex problem is broken down into smaller parts, which can then be sub divided into even smaller parts that can be solved more easily

Question 30

What is top down design?

Answer 30

* The breaking down of a computer system into a set of sub-systems. * Then breaking each sub-system down into a set of smaller sub-systems, until each sub-system just performs a single action * This hierarchy can then be represented using a structure diagram

Question 31

What are the 4 major components of a computer system?

Answer 31

* **inputs** -the data used by the system that needs to be entered while the system is active. * **processes** - the tasks that need to be performed using the input data and any stored data * **outputs** - information that needs to be displayed or printed for the users of the system * **storage** - data that needs to be stored in files on an appropriate medium for use in the future

Question 32

When writing computer programs why do we store data in a file?

Answer 32

* Any data stored in RAM will be lost when the computer is switched off * When data is saved to a file it is stored permanently * The data can then be accessed by the same program at a later date or accessed by another program

Question 33

Write some pseudocode that asks the user to enter their firstname and surname and then writes these to a text file called "UserDetails.txt" on separate line.

Answer 33

``` DECLARE surname : STRING DECLARE firstName: STRING DECLARE fileName : STRING filename <- "UserDetails.txt" OUTPUT "Please enter first name" INPUT firstName OUTPUT "Please enter surname" INPUT surname OPEN fileName FOR WRITE WRITEFILE fileName, firstName WRITEFILE fileName, surname CLOSEFILE (filename) ```

Question 34

A text file contains a username on the first line and a password on the second line. Write some pseudocode that reads the username and password from a text file called "UserDetails.txt" and then displays them on the screen

Answer 34

``` DECLARE username : STRING DECLARE password: STRING DECLARE fileName : STRING filename <- "UserDetails.txt" OPEN fileName FOR READ READFILE fileName, userName READFILE fileName, password CLOSEFILE (filename) OUTPUT username OUTPUT password ```

Question 35

Write some pseudcode to read the first line of a text file called "info.txt"

Answer 35

``` DECLARE fileName : STRING DECLARE line : STRING filename <- "info.txt" OPEN filename FOR READ READFILE fileName, line CLOSEFILE (filename) ```

Question 36

Write an algorithm to write the numbers 1 to 1000 to a text file named Numbers.txt

Answer 36

``` DECLARE fileName : STRING fileName <- "Numbers.txt" OPENFILE fileName FOR WRITE FOR i <- 1 TO 1000 STEP 1 WRITEFILE fileName, i NEXT i CLOSEFILE fileName ```

Question 37

Write an algorithm to read the first 100 student names from a text file named Names.txt. The data read in should be stored in an array of a suitable size

Answer 37

``` DECLARE studentNames : ARRAY[1:100] OF STRING DECLARE fileName : STRING fileName <- "Names.txt" OPENFILE fileName FOR READ FOR i <- 1 TO 100 STEP 1 READFILE fileName, studentNames[i] NEXT i CLOSEFILE fileName ```