Expression and Operartor In C Programming

This slide contain the introduction to the various operators and the expression available in C Programming Language.

1. Elements of Program Statements Operators Precedence & associativity Expression and Operators Compiled By: Kamal Acharya

2. Elements of a program Literals  fixed data written into a program Variables & constants  placeholders (in memory) for pieces of data Types  sets of possible values for data Expressions  combinations of operands (such as variables or even "smaller" expressions) and operators. They compute new values from old ones. Assignments  used to store values into variables Statements  "instructions". In C, any expression followed by a semicolon is a statement Compiled By: Kamal Acharya

3. Elements of a program Control-flow constructs  constructs that allow statements or groups of statements to be executed only when certain conditions hold or to be executed more than once. Functions  named blocks of statements that perform a well-defined operation. Libraries  collections of functions. Compiled By: Kamal Acharya

4. Statement Statements are elements in a program which (usually) ended up with semi-colon (;) e.g. below is a variables declaration statement int a, b, c ; Preprocessor directives (i.e. #include and define ) are not statements. They don’t use semi-colon Compiled By: Kamal Acharya

5. An expression statement is a statement that results a value Some examples of expression Value Literal expression e.g. 2, “A+”, ‘B’ The literal itself Variable expression e.g. Variable1 arithmetic expression e.g. 2 + 3 -1 The content of the variable The result of the operation Compiled By: Kamal Acharya

6. Operators Operators can be classified according to the type of their operands and of their output Arithmetic Relational Logical Bitwise the number of their operands Unary (one operand) Binary (two operands) Compiled By: Kamal Acharya

7. Binary expression Compiled By: Kamal Acharya

8. Unary Expression Compiled By: Kamal Acharya

9. Ternary Expression (a>2) ? 1: 0 Operator First operand is a condition Second operand is a value Third operand is another value Compiled By: Kamal Acharya

10. Arithmetic operators They operate on numbers and the result is a number. The type of the result depends on the types of the operands. If the types of the operands differ (e.g. an integer added to a floating point number), one is "promoted" to other. The "smaller" type is promoted to the "larger" one. char  int  float  double Compiled By: Kamal Acharya

11. Example of promotion: The result of the following “double division” is 2.5 5 / 2.0 Before the division process, 5 is promoted from integer 5 to float 5.0 The result of the following “integer division” is 2 5 / 2 There is no promotion occurred. Both operands are the same type. Compiled By: Kamal Acharya

12. Arithmetic operators: +, * + is the addition operator * is the multiplication operator They are both binary Compiled By: Kamal Acharya

13. Arithmetic operator:  This operator has two meanings: subtraction operator (binary) negation operator (unary) e.g. 31 - 2 e.g. -10 Compiled By: Kamal Acharya

14. Arithmetic operator: / The result of integer division is an integer: e.g. 5 / 2 is 2, not 2.5 Compiled By: Kamal Acharya

15. Arithmetic operator: % The modulus (remainder) operator. It computes the remainder after the first operand is divided by the second It is useful for making cycles of numbers: For an int variable x : if x is: 0 1 2 3 4 5 6 7 8 9 ... (x%4) is: 0 1 2 3 0 1 2 3 0 1 ... e.g. 5 % 2 is 1, 6 % 2 is 0 Compiled By: Kamal Acharya

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18. Relational operators These perform comparisons and the result is what is called a boolean: a value TRUE or FALSE FALSE is represented by 0; anything else is TRUE The relational operators are: < (less than) <= (less than or equal to) > (greater than) >= (greater than or equal to) == (equal to) != (not equal to) Compiled By: Kamal Acharya

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20. Logical operators (also called Boolean operators) These have Boolean operands and the result is also a Boolean. The basic Boolean operators are: && (logical AND) || (logical OR) ! (logical NOT) -- unary Compiled By: Kamal Acharya

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22. Assignment operator: = Binary operator used to assign a value to a variable. Compiled By: Kamal Acharya

23. Special assignment operators write a += b; instead of a = a + b; write a -= b; instead of a = a - b; write a *= b; instead of a = a * b; write a /= b; instead of a = a / b; write a %= b; instead of a = a % b; Compiled By: Kamal Acharya

24. Special assignment operators Increment, decrement operators: ++, -- Instead of a = a + 1 you can write a++ or ++a Instead of a = a - 1 you can write a-- or --a What is the difference? num = 10; ans = num++; num = 10; ans = ++num; First increment num, then assign num to ans. In the end, num is 11 ans is 11 First assign num to ans , then increment num. In the end, num is 11 ans is 10 post-increment pre-increment Compiled By: Kamal Acharya

25. Result of postfix Increment Compiled By: Kamal Acharya

26. Result of Prefix Increment Compiled By: Kamal Acharya

27. Precedence & associativity How would you evaluate the expression 17 - 8 * 2 ? Is it 17 - (8 * 2) or ( 17 - 8) * 2 ? These two forms give different results. We need rules! Compiled By: Kamal Acharya

28. Precedence & associativity When two operators compete for the same operand (e.g. in 17 - 8 * 2 the operators - and * compete for 8) the rules of precedence specify which operator wins. The operator with the higher precedence wins If both competing operators have the same precedence, then the rules of associativity determine the winner. Compiled By: Kamal Acharya

29. Precedence & associativity ! Unary – * / % + – < <= >= > = = != && || = higher precedence lower precedence Associativity: execute left-to-right ( except for = and unary – ) Compiled By: Kamal Acharya

30. Example: Left associativity 3 * 8 / 4 % 4 * 5 Compiled By: Kamal Acharya

31. Example: Right associativity a += b *= c-=5 Compiled By: Kamal Acharya

32. Precedence & associativity Examples: X =17 - 2 * 8 Ans : X=17-(2*8) , X=1 Y = 17 - 2 - 8 Ans : Y = (17-2)-8, Y=7 Z = 10 + 9 * ((8 + 7) % 6) + 5 * 4 % 3 *2 + 1 ? Not sure? Confused? then use parentheses in your code! Compiled By: Kamal Acharya

33. Sizeof () Operator C provides a unary operator named sizeof to find number of bytes needed to store an object. An expression of the form sizeof (object) returns an integer value that represents the number of bytes needed to store that object in memory. printf (“% d”,sizeof ( int )); /* prints 2 */ printf (“% d”,sizeof (char)); /* prints 1 */ printf (“% d”,sizeof (float)); /* prints 4 */ Compiled By: Kamal Acharya