Introduction to c  (Page 3/4)

Numeric constants of C are usually just the written version of numbers. For example 1, 0, 56.78, 12.3e-4. We can specify our constant in octal or hexadecimal, or force them to be treated as long integers.

• Octal constants are written with a leading zero : -0.15
• Hexadecimal constants are written with a leading 0x : 0x1ae
• Long constants are written with a trailing L : 890L or 890l

Character constants are usually just the character enclosed in single quotes; ‘a’, ‘b’, ‘c’. Some characters can’t be represented in this way, so we use a 2 character sequence (escape sequence).

Character constants participate in numeric operations just as any other integers (they are represented by their order in the ASCII character set), although they are most often used in comparison with other characters.

Character constants are rarely used, since string constants are more convenient. A string constant is a sequence of characters surrounded by double quotes e.g. “Brian and Dennis”.

A character is a different type to a single character string. This is important.

It is helpful to assign a descriptive name to a value that does not change later in the program. That is the value associated with the name is constant rather than variable, and thus such a name is referred to as symbolic constant or simply a constant.

Variables

Variables are the names that refer to sections of memory into which data can be stored.

Let’s imagine that memory is a series of different size boxes. The box size is memory storage area required in bytes.In order to use a box to store data, the box must be given a name, this process is known as declaration . It helps if you give a box a meaningful name that relates to the type of information and it is easier to find the data.The boxes must be of the correct size for the data type you are going to put into it. An integer number such as 2 requires a smaller box than a floating point number as 123e12.

Data is placed into a box by assigning the data to the box. By using the name of the box you can retrieve the box contents, some kind of data.

Variable named by an identifier. The conventions of identifiers were shown in 1.3.3.

Names should be meaningful or descriptive, for example, studentAge or student_age is more meaningful than age, and much more meaniful than a single letter such as a.

Operators

Programming languages have a set of operators that perform arithmetical operations , and others such as Boolean operations on truth values, and string operators manipulating strings of text. Computers are mathematical devices , but compilers and interpreters require a full syntactic theory of all operation in order to parse formulae involving any combination correctly.

Expressions

An expression in a programming language is a combination of values, functions, etc. interpreted according to the particular rules of precedence and association for a particular programming language, which computes and returns another value.