Ocr Computing As

Front 1

Name the 5 main datatypes, and how many bytes they are.

Back 1

1. String - depends on number of chars.
2. Char - 1 byte.
3. Integer - 4 bytes.
4. Double - 4 bytes.
5. Boolean - 1 byte.

Front 2

Define Array.

Back 2

Data structure that contains SEVERAL types of data of the same datatype under one identifier.

Front 3

When you are declaring an array, what would you need to write?

Back 3

1. Identifier of array - allows data to be accessed.
2. Size of array - enable locations that are next to eachother.
3. Datatype of contents - determine correct rules for manipulation.

Front 4

What are the advantages of using an array?

Back 4

1. Code is easier to manage as there are fewer variables.
2. Can use iteration when processing all elements in the array instead of dealing with each element separately.
3. Code will be easily scaleable by changing the size of the array.

Front 5

Write, in pseudo code, how you would initialise an array.

Back 5

FOR i=1 TO length of array
nameofArray(i) = 0
NEXT i

Front 6

Define 2D Array

Back 6

A data structure that stores MULTIPLE items of data of the same datatype under one identifier. It uses 2 index numbers and it can be represented in a table.

Front 7

Define Record.

Back 7

A data structure that can store together data items about a person or thing. The data items CAN be different datatypes.

Front 8

How would you estimate the size of a file?

Back 8

1. Add up the total for 1 record.
2. Multiply that number by the number of records.
3. Add an extra 10% for overheads.
4. Divide by 1000 to convert to kB.

Front 9

Name the types of file.

Back 9

1. Serial File.
2. Sequential File.
3. Indexed Sequential File.
4. Direct Access.
5. Random Files.

Front 10

What is a serial file?

Back 10

The data is stored in the order that it was entered.

Front 11

What is a sequential file?

Back 11

The data is stored according to a key field in the data.

Front 12

What is an indexed sequential file?

Back 12

The data is arranged with a key field but also has an index which is used to jump to certain blocks of data so records can be found quicker.

Front 13

What is direct access?

Back 13

If records in a sequential file have a fixed length then it may be possible to read the contents of a file directly if you know its position.

Front 14

What are random files?

Back 14

When records can be stored anywhere on a section of a disk.

Front 15

What are the advantages of a serial file?

Back 15

- Data can just be added to the end of a file.
- Easy to program.

Front 16

What are the disadvantages of a serial file?

Back 16

- When searching for data, you must start at the front and check each file one-by-one until you find the file you're looking for.
- If the item you want is at the end or not in the file at all, you would have to search through every single item before you can be certain.

Front 17

When would you use a serial file?

Back 17

- It doesn't matter what order the data is stored in.
- The data needs to be stored in the order that it's received.
- The data does not require searches to pick out individual records.

Front 18

When would you use a sequential file?

Back 18

- If it mattered what order the data should be in.
- You need to search for data frequently.

Front 19

What are the advantages of a sequential file?

Back 19

- Large files
- As accessing specific data will be quicker than using a serial search as you can skip over certain records.