Chapter2 Chapter2

Constants, Variables, Constants, Variables, and Data Typesand Data Types

2.1 Introduction2.1 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)

ObjectiveObjective• 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 set2.1 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 Tokens2.3 C Tokens• Keywords• Identifiers• Constants• Strings• Special symbols• operators

2.4 Keywords and Identifiers 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 Identifiers2.4 Keywords and Identifiers• Which of the following are valid

identifiers• Max first_name n1/n2• 3row double _34• Boy num girl-num

2.7 Data Types2.7 Data Types• Primary( fundamental) data types

– Integer– Floating point ( float and double )– Character– Void

• Fig.2.4 on page31

2.7 Data Types2.7 Data Types• Integer

– signed /unsigned• int• short int• long int

• Floating point – float– double– long double

• Character– signed / unsigned

• void

2.7 Data Types2.7 Data Types• Size and range of basic data types• Table 2.7 on page31• Table 2.8 on page32

2.5 Constants2.5 Constants• Integer• Real• Character• String

Integer constantsInteger 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

Integer constantInteger 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 constantInteger constant• Example2.1 Representation of integer constants on

a 16-bit computer.

#include<stdio.h>main(){

printf("Integer values\n\n");printf("%d %d %d\n",32767,32767+1,32767+10);printf("\n");printf("Long integer values\n\n");printf("%ld %ld %ld\n",32767L,32767+1L, 32767+10L);

}

Real constant (double)Real constant (double)• (1) decimal point

– Consist of 0 through 9, . ,+ , -– 3.14159, .94 , -.58 , +1.234

• (2)Exponential notationmantissa 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 constantCharacter 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’

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

• “x” and ’x’

2.6 variables2.6 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 variables2.8 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 variablesInitialization 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 statement2.10 Assignment statement• values can be assigned to variables

using the assignment operator = as

variable_name=value;

User-defined type declarationUser-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 TypesEnumerated 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;