This document discusses constants, variables, and data types in C programming. It covers the different types of constants like integer, real, character, and string constants. It also discusses variable declaration, initialization, and assignment. The main data types in C like integer, floating point, character, and void are described. It provides examples of declaring, initializing, and assigning values to variables of different data types in C.

1. Chapter2
Constants, Variables,
and Data Types

2. 2.1 Introduction
• In this chapter, we will discuss
– constants (integer, real, character,
string, enum) ,symbolic constants
– Variables (name, declare, assign)
– Fundamental data type ( int, float,
double, char, void)

3. Objective
• To be able to distinguish the
constants of different data type
• To be able to name, declare，
initialize and assign values to
variables
• To become familiar with fundamental
data types.

4. 2.1 Character set
• Letters
– uppercase A…Z
– lowercase a…z
• Digits :All decimal digits 0…9
• Special characters
– Table2.1 on page23
• White spaces

5. 2.3 C Tokens
• Keywords
• Identifiers
• Constants
• Strings
• Special symbols
• operators

6. 2.4 Keywords and Identifiers
• Keywords
– Table2.3 on page24
– Must in lowercase
• Identifiers
– User-defined names
– Consist of letters, underscore(_), and
digits
– First character must not be digit
– Can’t use a keyword
– Can’t contain white space

7. 2.4 Keywords and Identifiers
• Which of the following are valid
identifiers
• Max first_name n1/n2
• 3row double _34
• Boy num girl-num

8. 2.7 Data Types
• Primary( fundamental) data types
– Integer
– Floating point ( float and double )
– Character
– Void
• Fig.2.4 on page31

9. 2.7 Data Types
• Integer
– signed /unsigned
• int
• short int
• long int
• Floating point
– float
– double
– long double
• Character
– signed / unsigned
• void

10. 2.7 Data Types
• Size and range of basic data types
• Table 2.7 on page31
• Table 2.8 on page32

11. 2.5 Constants
• Integer
• Real
• Character
• String

12. Integer constants
• Decimal integer
– Consist of 0 through 9, +, -
• Octal integer
– Consist of 0 through 7, with a leading 0
• Hexadecimal integer
– Consist of 0 to 9, and a through f
preceded by 0x or 0X

13. Integer constant
• The largest integer value is machine-
dependent
• Qualifiers
– U or u: unsigned integer
– l or L: long integer
– UL or ul: unsigned long integer
– Short integer

14. • short is no longer than int and that
long is no shorter than int.

15. Integer constant
• Example2.1 Representation of integer constants on
a 16-bit computer.
#include<stdio.h>
main()
{
printf("Integer valuesnn");
printf("%d %d %dn",32767,32767+1,32767+10);
printf("n");
printf("Long integer valuesnn");
printf("%ld %ld %ldn",32767L,32767+1L,
32767+10L);
}

16. Real constant (double)
• (1) decimal point
– Consist of 0 through 9, . ,+ , -
– 3.14159, .94 , -.58 , +1.234
• (2)Exponential notation
mantissa e exponent
– .56e3 2.3e-3 -2.3E-3
– The exponent must be an integer number
• Suffixes f or F indicate a float constant
• L or l indicate a long double
• “Default values of constants” on page35

17. • Floating-Point Round-off Errors
• Take a number, add 1 to it, and
subtract the original number. What
do you get? You get 1. A floating-
point calculation, may give another
answer:

18. Character constant
• A character enclosed within ‘ ’
– ‘6’ ‘=‘ ‘;’ ‘ ‘
– Character constants have integer values,
For example
– ‘a’ and 97
– ‘0’ and 48
• Backslash character constants
– Table2.5 on page28
– ‘ooo’ and ‘xhh’

19. String constants
• a sequence of characters enclosed in
“ ”, for example
– “hello” “34” “+()” “x” “n”
• “x” and ’x’

20. 2.6 variables
• A variable is data name that may be
used to store a data value.
– Variable names correspond to locations
in the computer's memory
– Every variable has a name, a type, a
size and a value
– Whenever a new value is placed into a
variable, it replaces (and destroys) the
previous value
– Reading variables from memory does
not change them

21. 2.8 Declaration of variables
• The declaration of variables must be
done before they are used.
• declaration form
data-type v1,v2,…,vn;
• for example
– int count;
– float sum;
– double ratio;
– char ch;

22. Initialization of variables
• To initialize a variable means to
assign it a starting, or initial, value.
• In C, this can be done as part of the
declaration.
• char ch=‘ ’;
• int cows = 32,
• int dogs, cats = 94;

23. 2.10 Assignment statement
• values can be assigned to variables
using the assignment operator = as
variable_name=value;

24. User-defined type declaration
• the keyword “typedef” is used to
rename an existing data type.
typedef type identifier;
• for example
– typedef int integer;
– typedef float real;
– real sum1, sum2;
– integer count;

25. Enumerated Types
• You can use the enumerated type to
declare symbolic names to represent
integer constants.
• declarations:
– enum spectrum {red, orange, yellow,
green, blue, violet};
– enum spectrum color;