1 / 30

EEE 243B Applied Computer Programming

EEE 243B Applied Computer Programming. Expressions and Operators §3.1 – 3.4 Prof Sylvain P. Leblanc. Review. What are the four types found at the first level of the type hierarchy in C? What are the three Integral types and the Floating-point type we are concerned with?

ramya
Télécharger la présentation

EEE 243B Applied Computer Programming

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. EEE 243BApplied Computer Programming Expressions and Operators §3.1 – 3.4 Prof Sylvain P. Leblanc

  2. Review • What are the four types found at the first level of the type hierarchy in C? • What are the three Integraltypes and the Floating-point type we are concerned with? • What are the values of true and false for the bool type in C? • Why is it not a good idea to use literals (such as 0.07) in your code instead of a defined constant or a memory constant? Prof S.P. Leblanc

  3. Outline • Expressions in C • postfix • prefix • unary • binary • Assignments • Compound Assignments • Types Specific Operations • Operators, Precedence and Associativity • Side Effects Prof S.P. Leblanc

  4. A Caveat… • Because you have a knowledge of programming, in this course we concentrate on what makes C different than Matlab and other programming languages. • Some of what you will see in the next few weeks will be a review of what you already know with some syntactical differences. Prof S.P. Leblanc

  5. 1 - Expressions in C • There are two main things that separate C from many other programming languages: • Expressions • Pointers • Today we will look at the power that C provides to write expressions Prof S.P. Leblanc

  6. Expressions in C • An expression is a sequence of operands and operators that evaluates to a single value. • All the following are valid expressions • (a + b) • 4 + 5 • a++ • --c • x = a + b + c • y *= z • !(a > b || c) • -a Prof S.P. Leblanc

  7. 1 - Expressions in C Primary Identifier, constant, or parenthetical expression a, 5, (5+a–z) a++ ++b, !f, -a sizeof (int) 5 + 3, t || f x = y + 3 Ternary Will be discussed during next class Prof S.P. Leblanc

  8. The postfix expression • Operators that are placed after a variable form postfix expressions: • a++ , a-- • Example: if x is to have the value of a and then have a incremented after the assignment • In many languages: (initial value of a = 10) • x = a; //.. Value of a and x 10 • a = a + 1; //.. a = 11 • In C: • x = a++; // same result as above Prof S.P. Leblanc

  9. The prefix expressions • Operators that are placed before a variable form prefix expressions: • ++a, !a, -a • Example: if a is incremented and then assigned to x • In many languages: (initial value of a = 10) • a = a + 1; //.. a = 11 • x = a; //..Value of a and x 11 • In C: • x = ++a; // same result as above Prof S.P. Leblanc

  10. The unary expression • In unary expressions, operators can be placed before an expression (this is different from the prefix expression where the operator is placed before a variable) • sizeof() //also a unary expression • sizeof(int) • sizeof(x) • x = sizeof(3.1416) • sizeof((a + b -1)+(2-18.3)) • sizeof() looks like a function call but it is treated as an operator in that it has a different priority than a function call Prof S.P. Leblanc

  11. The binary expression • Operators that are placed between variables form binary expressions: • x + 1, y * 3 • A variable assignment is a form of binary expression: • x = 1, y = 3 Prof S.P. Leblanc

  12. Compound assignments • In MATLAB: the assignment operator is = • x = x + 1; y = y * 3; • ‘C’ has compound assignments for these operations Prof S.P. Leblanc

  13. Types Revisited • Remember that a type defines • a set of values and • a set of operations • Intrinsic types in C • void • char • bool • Integers • short int, int, long int, long longint • Floating point • float, double, long double • We will examine some of the type specific operations in C Prof S.P. Leblanc

  14. 2 - Type Specific Operations • ‘C’ includes a set of arithmetic, Boolean and logical operators • As just mentioned, the functionality of the operators depends upon type of data Arithmetic: + - * / % Boolean: & | ! && || ^ Logical: == != > < >= <= Prof S.P. Leblanc

  15. Valid void operators • void has no values and NO operators • void is very useful for pointers which we will cover later Operators: Prof S.P. Leblanc

  16. Valid bool Operators • The Boolean type (bool) is a recent addition to C • int is actually used for logical data • The use of the type bool requires the inclusion of stdbool.h • Defines bool, true and false • false is defined as int 0 • true is defined as int 1 (1 == 1) true (1 != 1) false (i = 0) false Prof S.P. Leblanc

  17. Valid Integer and char operator • Integers and char have the same set of valid operators Arithmetic: Addition + Subtraction – Multiplication * Division / Modulus % Pre/post incr ++ Pre/post decr -- Boolean: AND && OR || NOT ! Bitwise AND & Bitwise OR | Bitwise XOR ^ Prof S.P. Leblanc

  18. Valid Integer and char operator • Integers and char have the same set of valid operators Logical: Greater than > Greater than or equal >= Less Than < Less Than or equal <= Equal to == Not Equal != WARNING: = and == are NOT THE SAME Prof S.P. Leblanc

  19. Notes on Integer Operators • % Modulus • Returns the remainder of an INTEGER division • Ex: knowing that 7/4 = 1 remainder 3 • 7%4 returns a value of 3 • 7/4 returns a value of 1 • Power: THERE is NO POWER OPERATOR IN ‘C’ • ^ is a bitwise XOR • In MATLAB for x2 we can code it as • x^2 • In C for x2 we can code it as • x*x NOTE: There is a pow() function in <math.h> Prof S.P. Leblanc

  20. Valid floating point operators • Floating point values have the following valid operators Arithmetic: Addition + Subtraction – Multiplication * Division / Modulus % Pre/post incr ++ Pre/post decr -- Boolean: AND && OR || NOT ! Bitwise AND & Bitwise OR | Bitwise XOR ^ Prof S.P. Leblanc

  21. Floating point logical operators • Floating point values have the following valid operators Logical: >, >=, <, <=, !=, == Warning: == It is not recommended to use == for float types 1.1e-19 does not exactly equal 0 It is recommended to use a range fabs(x)<1e-7 Prof S.P. Leblanc

  22. 3 - Precedence of operators • From your CSE101 introductory programming course, you will know many of the operators that you will need during this course • Except for the bit, address and pointer operators • If there are several operators in an expression the precedence determines the order in which the operators are evaluated • If you cannot remember, there is a table on the inside cover of Forouzan. Prof S.P. Leblanc

  23. 4 - Associativity • Associativity is used to determine the order in which operators of the same precedence are evaluated in complex expressions • Most expressions use left-to-right associativity: • 3 * 8 / 4 % 4 * 5 is equivalent to • ((((3*8)/4)%4)*5) Prof S.P. Leblanc

  24. Right-to-Left Associativity • Right-to-left associativity is used only for three types of expressions: • Unary (simple case), • Ternary (next class), and • Assignment expression associativity • a+=b*=c-=5 Is the same as: • (a=a+(b=b*(c=c–5))) Prof S.P. Leblanc

  25. Operators, Precedence & Associativity • Always remember: first precedence than associativity • If you look at the precedence table, parenthetical expressions are at the top of the food chain. • When in doubt about the order of evaluation of any expression, use parentheses • The good thing about using the parentheses is … the compiler checks them! Prof S.P. Leblanc

  26. 4 - Side Effects • Some of the operators modify the value in memory of the variable they operate on • This modification of memory content is called a side effect • For example, x = ++a; has 2 side effects • a is pre-incremented • x is ‘assigned’ the new value of ‘a’ Prof S.P. Leblanc

  27. Practice Problems • Questions involving precedence and evaluating expressions are VERY OFTEN on the MIDTERM TEST and FINAL EXAM • Should you choose to complete the following, I will mark them: • 3.17 • 3.22 • 3.23 (assume int x, y, z) • 3.23 (assume float x, y, z) • 3.24 Prof S.P. Leblanc

  28. Practice Problems (Continued) • If originally a=2, b=5, c=1and d= -1, what is the value of each of the following expressions? (if inta,b,c,d; ) • a=b+=c+d • c=d+=a*=b%=3 • a+=(a==b)*c*=-2+d; • a>b + b>c + c>d + d>a • For char a =’d’; int b=6; float c = 3.161524; what are the values of the following expressions? • char d; • int e; • float f; • d = a*b; • e = a*b; • d= a*c; • e=a*c • f = a*c; • f =c%2; Prof S.P. Leblanc

  29. Quiz Time • What is the value of this expressions • 4 + 2 * 5 • If a = 3 and b = 5 what are their value after: • x = --a + b++ • b += a-- • y = -b++ Prof S.P. Leblanc

  30. Next Lecture • Mixed Expressions and Blocks Prof S.P. Leblanc

More Related