Chapter2 Constants, Variables, and Data Types

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)

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.

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

2.3 C Tokens Keywords Identifiers Constants Strings Special symbols operators

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

2.4 Keywords and Identifiers Which of the following are valid identifiers Maxfirst_namen1/n2 3rowdouble_34 Boy numgirl-num

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

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

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

2.5 Constants Integer Real Character String

Integer constants Decimal integer –Consist of 0 through 9, +, - Octal integer –Consist of 0 through 7, with a leading 0 Hexadecimal integer –Consist of0 to 9, and a through f preceded by 0x or 0X

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

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

Integer constant Example2.1 Representation of integer constants on a 16-bit computer. #include main() { printf("Integer values\n\n"); printf("%d %d %d\n",32767, , ); printf("\n"); printf("Long integer values\n\n"); printf("%ld %ld %ld\n",32767L, L, L); }

Real constant (double) (1) decimal point –Consist of 0 through 9,.,+, - – ,.94, -.58, (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

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:

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

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

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

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;

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;

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

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;

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;