Introduction to Computing – B142L

Data types

Academic year 2011/12



Objectives:

1. Basic data types in the C language
2. Comparison of different data types

Digital data

A bit is the smallest unit of digital data. There are two possible values:

• zero = switch off = low voltage
• one = switch on = high voltage

A combination of multiple bits can be used to store and encode more complex and useful data.

• 8 bits = 1 byte
• 16 bits = 2 bytes = 1 word

Binary encoding of numeric data

The sum of binary encoded bits can be used to represent integer (whole number) values.

Binary encoding of characters

ASCII (American Standard Code for Information Interchange) is a standard for using binary encoding to represent character symbols.

ASCII uses 8 bits to encode 128 characters:

• 0–31 = control characters
• 32–63 = numbers and punctuation
• 64–95 = uppercase letters
• 96–127 = lowercase letters

Part of the table of ASCII codes:

Basic data types

There are 3 basic data type categories in the C language.

1. void
2. integer
   • char = 1 byte
     • unsigned char
   • short = 2 bytes
     • unsigned short
   • int = 4 bytes
     • unsigned int
   • long = 8 bytes
     • unsigned long
3. floating point
   • float = 4 bytes = 6 digits of decimal precision
   • double = 8 bytes = 15 digits of decimal precision
   • long double = 16 bytes = 18 digits of decimal precision

Basic data types

Data type indicates:

1. The amount of memory to allocate, and
2. How to interpret the bits of data stored at the allocated location in memory

Data types increases portability of software between different hardware.

They are reserved keywords in C.

Data variables

A data variable has:

1. an identifier
2. a data type
3. a data value

Identifiers in the C language

Identifiers are user friendly names of variables, functions and constants. They are case sensitive and have no length restrictions. However, they must follow these rules:

• First character must not be a digit
• Consists of a sequence of letters (A-Z, a-z), digits (0-9) and underscores (_)

Boolean values

The C language does not have a data type for boolean values of true and false. Instead, it uses the following rules:

• Any value equal to zero is considered to be equivalent to boolean value false.
• Any value not equal to zero is considered to be equivalent to boolean value true.

Review questions

---

Data types

What is the decimal value of the binary number below?

High order   0 0 1 1 0 0 1 0   Low order

50
76
77
51

Average rating is  

Review questions

---

Data types

Which is not a valid data type keyword in the C language?

integer
short
double
float

Average rating is  

Review questions

---

Data types

Which is not a basic data type category in the C language?

floating point
double
integer
void