2.2 Variables, constants, inputs, outputs and assignments

Question 1

What is a variable?

Answer 1

A value stored in memory that can change while the program is running

Question 2

What is a constant?

Answer 2

A value that does not change while the program is running, and is assigned when the program is designed

Question 3

What is assignment?

Answer 3

Giving a variable or constant a value

Question 4

What is casting?

Answer 4

• Converting a variable from one data type to another e.g. integer to a string
• A variable can be an integer, character, string, real (float), or Boolean

Question 5

What is an input?

Answer 5

A value is read from an input device e.g. keyboard

Question 6

What is an output?

Answer 6

Data generated by the computer and displayed to the user

Question 7

What are the advantages of constants?

Answer 7

• Constants make a program easier to read as they are usually declared and assigned at the top of the program
• Constants can easily be changed by the programmer in one place in a program
• Instead of changing every instance of a value throughout a program
• This leads to less chance of errors
• The compiler can optimise the code - this makes a program run more quickly if constants are used instead of variables

Question 8

Why is casting needed?

Answer 8

• Casting changes a variable from one data type to another e.g. a string to an integer
• Inputs from the keyboard are always characters. Multiple characters are called a string
• However to perform an addition, the ALU must use numbers - therefore a string must be cast to a number