1 Operators And Expressions

2 Operators Arithmetic Operators Relational and Logical Operators Special Operators

3 Arithmetic Operators OperatorAction –Subtraction, also unary minus +Addition *Multiplication /Division %Modulus --Decrement ++Increment

4 Precedence and Associativity Precedence of the Arithmetic operators: High (unary minus) * / % Low+ - - a * b – c((- a) * b) – c

5 inside parenthesesExpressions inside parentheses are evaluated first. 1 * (2 - 3) Operators on the same level of precedence are evaluated from left to right. (Associativity) –5 (((1 + 2) + 3) + 4) –5

6 Increment & Decrement Operators Provide a concise notation for incrementing or decrementing a variable by 1. Are unary operators. ++x or x++ --x or x-- Can be applied to variables but not to constants or ordinary expressions. ++i;legal cnt--;legal 777++;illegal ++(a * b -1); illegal

7 May either prefix or postfix the operand. Prefix++x; or Postfixx++; x = x + 1; ++ & -- both cause a value of a variable to change in memory. ( Have a side effect).

8 Increment Postfix: i++; Expression value is the current value (Before you increment) then it increments. “use - then increment” Increment Prefix:++i; Expression value is the value After you increment. “increment - then use” Decrement Postfix:i--; “use - then decrement” Decrement Prefix:--i; “decrement - then use”

9 Examples x =10;y = ++x; y 11 x =10;y = x++; y 10 int i = 3, j = 2, k; i++;i j = ++i;ji k = i++;k i k = (--j+3) kj

10 l = 4; n = 3; m = 2; x = l * n + m++;x After the assignment to x. m 14 3

11 int a, b, c=0; a = ++c; b = c++; a = ? b = ? c= ? int b = 2, d = 4; 7--b*++d 7-((-b)*(++d)) ? int j = 2, k = 3, m = 4; j*=k=m+5 j=(j*(k=(m+5))) ?

12 int a,b; a = 1; b = 12; printf (“a+++b = %d/n”, a+++b); a = 1; b = 12; printf (“a++ +b = %d/n”, a++ +b); a = 1; b = 12; printf (“a+ ++b =% d/n”, a+ ++b);

13 Relational and Logical Operators Relational refer to the relationship that value can have with one another. Logical refers to the ways these relationships can be connected. True is any value other than zero. False is zero.

14 Relational Operators: OperatorAction >Greater than >=Greater than or equal <Less than <=Less than or equal = =Equal !=Not equal Logical Operators: OperatorAction &&AND ||OR !NOT

15 The truth table for the logical operators. True(1), False(0). pqp&&qp || q!p

16 Precedence and Associativity High! > >= < <= = = != && Low|| !0&&0||0 ((!0)&&0)||0 FALSE

17 Both are lower in precedence than the arithmetic operators. 10 > > (1 + 12) FALSE 0 Associativity left to right. int x; x = 100; printf(''%d", x>10); __?

18 !A is false (0) if A’s value is: __. is true (1) if A’s value is: __. !!5 ! (!5)! (0) 1 NOT (Any NON-zero)0 5 && 3 ? Examples

19 inti, j = 1; j = j && (i = 2); 1) (i=2)i 2) &&j && 2 true && true1 3) =j ( ) needed

20 ji j = j && (i = = 3); 1) (i = = 3) false0 2) && j&& 0 0 3) = j ( ) not needed

21 ji j = j || (i/2) 1) (i/2)(2/2) 1 2) ||j|| 1true1 3) =j ( ) not needed

22 ji j = !j && (i = i + 1); 1)i )=i 3)!!j !1 0 4)&&0 && 3 5)=j

23 The Comma Operator lLowest precedence of all the operators. lCauses a sequence of operations, “do this and this and this…”. lIs a binary operator. expression_1, expression_2 lAssociates left to right. expression_1 is evaluated first expression_2 is evaluated second x = (y=3, y+1); x 4 ( ) needed

24 l The Comma Expression as a whole has the value and type of expression_2. inti = 2; j = 4; j = i++, i - j; * i * j(3-4) 3

25 It allows multiple initializations and multiple processing of indices. for (sum=0, i=1; i<=n; ++i) sum += i; Comma Operators can be useful in control statements though many “C” advocates discourage their use.

26 e.g.int i; i = 0; for ( ; i < 10; putchar (‘a’ + i), i++); will output?  3rd expression in the for statement is a comma expression.  putchar is called,executed.Then i is increased.  Most commas in a program DO NOT represent comma operators. see text - pg. 99

27 The ( ) and [ ] Operators Parentheses are operators that increase the precedence of the operations inside them. Square brackets perform array indexing (See Chapter 9 for a discussion of array.) int main(void) { char s[80]; s[3] = 'X'; printf(''%c", s[3]); return 0; }

28 The Conditional Operator ? Ternary operator. A powerful and convenient operator that replaces certain statements of the if-then- else form. Exp1 ? Exp2: Exp3 Stands for:if Exp1 then Exp2 else Exp3

29 x = 10; y = x>9 ? 100 : 200; x = 10; if(x>9) y = 100; else y = 200; Examples

30 int i, h, j = 2; i = (j==2) ? 1:3; k = (i>j) ? i:j; ( ) not needed i get 1 k get max of I or j

31 This statement does what? c = (c > =‘a’ && c < = ‘z’) ? c - (‘z’ - ‘Z’):c; IF True - have a Lower case letter in the variable “C”. Exper2: c - (‘z’ - ‘Z’) will give Capital Letter of whatever is in C. e.g. a - (‘z’ - ‘Z’) 97 - (122 – 90) = 65 which is ‘A’. IF False – Capital Letter and leaves it alone.

32 Expressions An expression in C is any valid combination of operators, constants, functions and variables. An statement is a valid expression followed by a semicolon. func(); /* a function call */ a = b+c; /* an assignment statement */ b+f(); /* a valid, but strange statement */ ; /* an NULL statement */

33 Null Statement:; [A semi-colon alone by itself]. Can be useful in loops & conditional statements. The body of a loop could be empty. Scanf(“%d”, &x); While(printf(“%d”,x),scanf(“%d”,&x)==1) ;

34 Spacing and Parentheses Redundant or additional parentheses do not cause errors or slow down the execution of an expression. x=10/y-(127/x); x = y/3-34*temp+127; x = (y/3) - (34*temp) + 127;