Bài giảng Lập trình C - Session 2: Variables and Data Types

Variables and Data Types Session 2 Elementary Programming with C/Session 2/ * of 22 Objectives Discuss variables Differentiate between variables and constants List the different data types and make use of them in C programs Discuss arithmetic operators Elementary Programming with C/Session 2/ * of 22 Variables Data Memory Each location in the memory is unique Variables allow to provide a meaningful name for the location in memory 15 Elementary Programming with C/Session 2/ * of 22 Example A, B and C are variables in the pseudocode Variable names takes away the need for a programmer to access memory locations using their address The operating system takes care of allocating space for the variables To refer to the value in the memory space, we need to only use the variable name Elementary Programming with C/Session 2/ * of 22 Constants A constant is a value whose worth never changes Examples 5 	numeric / integer constant 5.3	numeric / float constant ‘Black’ 	string constant ‘C’	Character constant Variables hold constant values Elementary Programming with C/Session 2/ * of 22 The names of variables, functions, labels, and various other user defined objects are called identifiers Some correct identifier names arena s_count marks40 class_one Examples of erroneous identifiers 1sttest oh!god start... end Identifiers can be of any convenient length, but the number of characters in a variable that are recognized by a compiler varies from compiler to compiler Identifiers in C are case sensitive Identifier Names ! is invalid Elementary Programming with C/Session 2/ * of 22 Guidelines for Naming Identifiers Elementary Programming with C/Session 2/ * of 22 Keywords Keywords : All languages reserve certain words for their internal use Keywords hold a special meaning within the context of the particular language No problem of conflict as long as the keyword and the variable name can be distinguished. For example, having integer as a variable name is perfectly valid even though it contains the keyword int Elementary Programming with C/Session 2/ * of 22 Data Types-1 Different types of data are stored in variables. Some examples are: Numbers Whole numbers. For example, 10 or 178993455 Real numbers. For example, 15.22 or 15463452.25 Positive numbers Negative numbers Names. For example, John Logical values. For example, Y or N Elementary Programming with C/Session 2/ * of 22 Data Types-2 Datatype variableName A data type describes the kind of data that will fit into a variable The name of the variable is preceded with the data type For example, the data type int would precede the name varName int varName Elementary Programming with C/Session 2/ * of 22 void char double Basic Data Types The basic data types are float int Elementary Programming with C/Session 2/ * of 22 Type int Stores numeric data	 	int num; Cannot then store any other type of data like “Alan” or “abc” 16 bits (2 bytes) Integers in the range -32768 to 32767 Examples: 12322, 0, -232 Elementary Programming with C/Session 2/ * of 22 Type float Stores values containing decimal places 	 	 	float num; Precision of upto 6 digits 32 bits (4 bytes) of memory Examples: 23.05, 56.5, 32 Elementary Programming with C/Session 2/ * of 22 Type double Stores values containing decimal places 	 	 	double num; Precision of upto 10 digits 64 bits (8 bytes) of memory Examples: 2.0, 3.55, 100000 Elementary Programming with C/Session 2/ * of 22 Type char Stores a single character of information 	 	 	char gender; 	gender='M'; 8 bits (1 byte) of memory Examples: ‘a’, ‘m’, ‘$’ ‘%’ , ‘1’, ’5’ Elementary Programming with C/Session 2/ * of 22 Type void Stores nothing 	 Indicates the compiler that there is nothing to expect Elementary Programming with C/Session 2/ * of 22 Derived Data Types Derived data type Basic Data types Data type Modifiers Elementary Programming with C/Session 2/ * of 22 signed and unsigned Types unsigned type specifies that a variable can take only positive values unsigned int varNum; varNum=23123; varNum is allocated 2 bytes modifier may be used with the int and float data types unsigned int supports range from 0 to 65535 Elementary Programming with C/Session 2/ * of 22 long and short Types short int occupies 8 bits (1 byte) allows numbers in the range -128 to 127 long int occupies 32 bits (4 bytes) -2,147,483,647 and 2,147,483,647 long double occupies 128 bits (16 bytes) Elementary Programming with C/Session 2/ * of 22 Data Types and their range-1 Elementary Programming with C/Session 2/ * of 22 Data Types and their range-2 Elementary Programming with C/Session 2/ * of 22 Sample Declaration 	main () 	{ 	char abc;	 /*abc of type character */ 	int xyz;	 /*xyz of type integer */ 	float length; /*length of type float */ 	double area;	 /*area of type double */ 	long liteyrs; /*liteyrs of type long int */ 	short arm;	 /*arm of type short integer*/ 	}