Understanding Variables, Operators, and Expressions in C++

1. Lecture 1 Variable, Operators and Expressions

2. Variable • In C++ a variable is a place to store information. • A variable is a location in your computer memory in which you can store a value and from with you can later retrieve the value. • Every variable has a name, type and value

3. When a variable in C++ is defined, you must tell the compiler what kind of variable is it. (integer, character etc) • This information tells the compiler how much room to set aside and what kind of value you want to store in your variable.

4. Basic Data Types • Following are the five Basic Data Types: Size • Int • char • float • double • void

5. TYPE int • Stores only numeric data • It cannot store decimal numbers with fractional part. E.g 1.4 and 14.0 • (-) sign must be written when using negative number but with positive number (+) sign is not mandatory. • Leading zeros and commas cannot be used when writing integers.

6. TYPE int(cont..) • The storage space occupied by int data type depends on the operating system, compiler and microprocessor. (4bytes or 2bytes) int sample values 4578 -4578 0

7. TYPE char • Stores character data, which includes letters, digits, and special symbols. • Char data occupies 1byte of memory space • A character variable can store only one character at a time. • Char must be enclose in single quotation marks. char sample values ‘B’ ‘d’ ‘4’ ‘?’ ‘*’

8. TYPE float and double • To store decimal numbers, float data type is used. • Occupies 4 bytes. • Floating value are precise up to 5-6 digits where as double provides 10 digits precision.

9. Naming Variables (identifier) • A variable name is combination of alphabet, digits, or underscore. • The first character in the variable name must be an alphabet. • No commas or blanks are allowed within a variable name. • No special symbols other than underscore can be used in a variable name.

10. Correct or Incorrect Name • X • Abc124 • My variable • 124abc • My ^ Variable • My_Variable • MyVariable • My Varibale!

11. What Does a Variable Declaration Do? int ageOfDog; A declaration tells the compiler to allocate enough memory to hold a value of this data type, and to associate the identifier with this location. 4 bytes for ageOfDog

12. Syntax for Declarations Variable Declaration Datatype (variable) TypeName Identifier , Identifier . . ;

13. Example1Variable Declaration and Initialization int main( ) { int x=5; int y; y=5; cout<< “The value of x and y”<<x<<y; } What is initialization :

14. Example 2Receiving keyboard input and screen output //include iostream + conio header files int main( ) { int myage; cout<<“ Enter your age”; cin>>myage; cout<<myage; }

15. Constants • A constant is the quantity that does not change. This quantity can be stored at a location in the memory. • A variable can be considered as the name given to the location in memory where constant is stored. • Key words : Reserve words for C

16. Memory Depiction float y = 12.5;

17. Memory Depiction float y = 12.5; int Temperature = 32;

18. Memory Depiction float y = 12.5; int Temperature = 32; char Letter = 'c';

19. Memory Depiction float y = 12.5; int Temperature = 32; char Letter = 'c'; int Number;

20. Constants Keyword #include <stdio.h> const float PI = 3.14159; int main() { printf("Hello, world\n %d", XYZ); getch(); return 0; }

21. OPERATORS

22. In C++ you can combine variables and/or numbers using the arithmetic operators.

23. Arithmetic in C C operation Algebraic C Addition(+) f+7 f+7 Subtraction (-) p-c p-c Multiplication(*) bm b*m Division(/) x/y, x ,x y x/y Modulus(%) r mod s r%s Power (Exponent) xy x ^ y y

24. Assignment Statement • The assignment statement takes the form: • variable = expression; • Expression is evaluated and its value is assigned to the variable on the left side • In C++ = is called the assignment operator. • Integer division truncates remainder • Variable = 7 / 5 ; • 7 / 5 evaluates to 1 • Modulus operator returns the remainder • 7 % 5 evaluates to 2 • SomeVar = 7 % 5;

25. Definition int NewStudents = 6;

26. Definition int NewStudents = 6; int OldStudents = 21;

27. Definition int NewStudents = 6; int OldStudents = 21; int TotalStudents;

28. Assignment Statement int NewStudents = 6; int OldStudents = 21; int TotalStudents; TotalStudents = NewStudents + OldStudents;

29. Assignment Statement int NewStudents = 6; int OldStudents = 21; int TotalStudents; TotalStudents = NewStudents + OldStudents;

30. Assignment Statement int NewStudents = 6; int OldStudents = 21; int TotalStudents; TotalStudents = NewStudents + OldStudents; OldStudents = TotalStudents;

31. Assignment Statement int NewStudents = 6; int OldStudents = 21; int TotalStudents; TotalStudents = NewStudents + OldStudents; OldStudents = TotalStudents;

33. Assignment Statement sum = 5 + 3; sum= num1 + num2; sum= 2 + num1;

34. More Assignment Statement • There is a shorthand notion that combines the assignment operator (=) and an arithmetic operator so that a given variable can have its value changed by adding, subtracting, multiplying, or dividing by a special value. • Variable Operator = Expression • Same as • Variable = Variable Operator (Expression)

35. Examples • count += 2; // count = count + 2; • count -= 2; // count = count - 2; • count *= 2; • count *= val1 + val2; // count = count*val1 + val2 • count =+ 2; // count = 2+ count;

36. Precedence order • Highest to lowest • () • *, /, % • +, -

37. Example Algebra: z = pr%q+w/x-y C: z = p * r % q + w / x – y ; Precedence: 1 2 4 3 5

38. Evaluate the Expression 7 * 10 - 5 % 3 * 4 + 9

39. Evaluate the Expression 7 * 10 - 5 % 3 * 4 + 9 means (7 * 10) - 5 % 3 * 4 + 9 70 - 5 % 3 * 4 + 9 70 - (5 % 3) * 4 + 9 70 - 2 * 4 + 9 70 - (2 * 4) + 9 70 - 8 + 9 (70 - 8) + 9 62 + 9 71 What would be the precedence of parenthesis: Evaluate (4+5)/5-10%4

40. EXAMPLE :

41. Increment & Decrement Operators • Increment operator: increment variable by 1 • Decrement operator: decrement variable by 1 • Pre-increment: ++variable • Post-increment: variable++ • Pre-decrement: --variable • Post-decrement: variable— • Int x; : ++x; : cout<<x++; x++; : x = x + 1; : cout<<++x;x--;

42. Decision Making • Checking falsity or truth of a statement • Equality operators have lower precedence than relational operators • Relational operators have same precedence • Both associate from left to right

43. Decision Making • Equality operators • == • != • Relational operators • < • > • <= • >=

44. Summary of precedence order Operator Associativity () left to right * / % left to right + - left to right < <= > >= left to right == != left to right = left to right