Constants and Variables

Transcription

1 DATA STORAGE

2 Constants and Variables In many introductory courses you will come across characteristics or elements such as rates, outputs, income, etc., measured by numerical values. Some of these will always remain the same, and some will change. The characteristic or element that remains the same is called a constant. For example, the number of donuts in a dozen is always 12. That means the number of donuts in a dozen is a constant. While some of these characteristics or elements remain the same, some of these values can vary (e.g., the price of a dozen donuts can change from $2.50 to $3.00), we call these characteristics or elements variables. Variable is the generic term for any characteristic or element that changes. You should be able to determine which characteristics or elements are constants and which are variables.

3 Example Which of the following are variables and which are constants? The temperature outside your house. The number of square feet in a room that is 12 ft by 12 ft The noise level at a concert or class. Price of a gallon of gas. Number of inches in a foot. Number of leaves on a tree. Capacity of the gas tank of your car.

4 Data Types A data type is a set of values together with operations (functions) on that set. E.g. the set of real numbers together with the operations +,,, /. Often one has a system of data types, i.e. multiple named sets and operations that can have input and output values from different sets. E.g. < is an operation that takes two numbers and returns a Boolean value (true or false).

5 Implementation Implementations of data types on computers are often limited. If the result of an operation falls outside the implemented subset, the result is undefined. E.g.: The program is aborted with an error message. The program continues to work, but with a wrong value. E.g. adding two large positive numbers gives a negative number.

6 Data Types Primary Data Types Void Character Integer Floating Boolean Composite Data Types Array String Pointer Structure Union Enum etc.

7 Operators An operator is a symbol (+,-,*,/) that directs the computer to perform certain mathematical or logical manipulations and is usually used to manipulate data and variables Ex: a+b 1. Arithmetic operators 2. Relational operators 3. Logical operators 4. Assignment operators 5. Increment and decrement operators 6. Conditional operators 7. Bitwise operators 8. Special operators

8 Arithmetic Operators

9 Relational Operators

10 Logical Operators Logical expression or a compound relational expression An expression that combines two or more relational expressions Ex: if (a==b && b==c)

11 Truth Table

12 Assignment Operators Syntax: v op = exp; Where v = variable, op = shorthand assignment operator exp = expression Ex: x=x+3 x+=3

13 Shorthand Assignment Operators

14 Increment & Decrement Operators 2 useful operators namely Increment ++ Decrement operators The ++ operator adds a value 1 to the operand The -- operator subtracts 1 from the operand ++a or a++ --a or a--

15 Rules for ++ & -- Operators 1. These require variables as their operands 2. When postfix either ++ or is used with the variable in a given expression, the expression is evaluated first and then it is incremented or decremented by one 3. When prefix either ++ or is used with the variable in a given expression, it is incremented or decremented by one first and then the expression is evaluated with the new value

16 Examples for ++ & -- operators Let the value of a =5 and b=++a then a = b =6 Let the value of a = 5 and b=a++ then a =6 but b=5 i.e.: 1. a prefix operator first adds 1 to the operand and then the result is assigned to the variable on the left 2. a postfix operator first assigns the value to the variable on left and then increments the operand.

17 Conditional Operators Syntax: exp1? exp2 : exp3 Where exp1,exp2 and exp3 are expressions Working of the? Operator: Exp1 is evaluated first, if it is nonzero(1/true) then the expression2 is evaluated and this becomes the value of the expression, If exp1 is false(0/zero) exp3 is evaluated and its value becomes the value of the expression Ex: m=2; n=3 r=(m>n)? m : n;

18 Bitwise Operators These operators allow manipulation of data at the bit level

19 Arithmetic Expressions ab c a b S= a b 2 c

20 Rules for evaluation of expression 1. First parenthesized sub expression from left to right are evaluated. 2. If parentheses are nested, the evaluation begins with the innermost sub expression 3. The precedence rule is applied in determining the order of application of operators in evaluating sub expressions 4. The associatively rule is applied when 2 or more operators of the same precedence level appear in a sub expression. 5. Arithmetic expressions are evaluated from left to right using the rules of precedence 6. When parentheses are used, the expressions within parentheses assume highest priority

21 Example Evaluate the expression when a=4 b=a- ++a =a 5 =5-5 =0