ECE 103 Engineering Programming Chapter 4 Operators Herbert G. Mayer, PSU Status 6/10/2016 Initial content copied verbatim from ECE 103 material developed by Professor Phillip PSU ECE

Syllabus Operator Precedence and Associativity Arithmetic Operators Relational and Logical Operators Increment and Decrement Operators Assignment Operators Type Conversion (Casting) Memory Access Operators

2 Operator Precedence and Associativity Operators perform very basic arithmetic, comparison, and logic operations. When operators are combined, rules of precedence and associativity determine the evaluation order. Precedence Rules → specifies which operator is evaluated first when operators of different precedence are adjacent Associativity Rules → specifies which operator is evaluated first when operators of the same precedence are adjacent

3 Table 1: C Operator Precedence Table LDescriptionOperatorAssociativityLDescriptionOperatorAssociativity 1 Function call ( ) left-to-right 5 Bitwise left shift << left-to-right Array subscript [ ] Bitwise right shift >> Struct member. 6 Less than < left-to-right Struct dereference -> Greater than > Increment (post) expr++ LT or equal to <= Decrement (post) expr-- GT or equal to >= 2 Indirection * right-to-left 7 Equal to == left-to-right Reference (addr) & Not equal to != Unary plus + 8Bitwise AND & left-to-right Unary minus - 9Bitwise XOR ^ left-to-right Logical negation ! 10Bitwise OR | left-to-right Bitwise NOT ~ 11Logical AND && left-to-right Increment (pre) ++expr 12Logical OR || left-to-right Decrement (pre) --expr 13Conditional ? : right-to-left Cast ( type ) 14Assignment = += -= *= /= %= >>= <<= &= ^= |= right-to-left Size in bytes sizeof 3 Multiplication * left-to-right 15Comma, left-to-right Division / Highest precedence is Level 1. Lowest precedence is Level 15. Use parentheses () to alter the order of evaluation. Modulo % 4 Addition + left-to-right Subtraction -

4 Arithmetic Operators The C language does not support element-by-element operators (e.g., like the.* or.^ operators in MATLAB). OperatorDescriptionExample (Base 10) Unary + Denotes positive value+3 Unary - Denotes negative value -3-3 * Multiplication12 * 4 is 48 / Division12 / 4 is 3 % Modulus (remainder)12 % 4 is 0, 12 % 5 is 2 + Addition is 16 - Subtraction is 8

5 C lacks a built-in “raise to a power” operator. Include the header file. Use the math library function called pow. Syntax: pow(base, exponent) returns base exponent Example: 2.2+(3.5) 3 → *3.5*3.5 -or pow(3.5, 3) Example: y (x+1)/2.8 → pow(y,(x+1)/2.8)

6 Note: Do not use pow() solely to express a numeric constant in base 10 scientific notation. Example: 1.25  10 3 should be written as 1.25e3 in C code. Although 1.25*pow(10,3) works, it is inefficient. Example: 5.3  should be written as 5.3e-5 in C code. Example: 2  3 8 is not base 10, so the e notation cannot be used. Instead, 2*pow(3,8) is correct usage here. Example: 6.5  10 X is base 10 but not a constant. Use 6.5*pow(10,X).

7 Relational and Logical Operators TypeOperatorDescription Relational (comparing values) < Less than > Greater than <= Less than or equal to >= Greater than or equal to == Equal to != Not equal to Logical (Boolean logic) ! Logical negation && Logical AND (short-circuit) || Logical OR (short-circuit)

8 expression  a valid combination of constants, variables, function calls, and operators that, when evaluated, produces a value. The numeric value of a relational or logical expression is: 1 if the expression is true 0 if the expression is false

9 Example: w = 5+sin(3.14) / 2.75; → x = 123 – (10*w); → t1 = w >= 5; → 1 (i.e., true) t3 = x > 0 && w < 5; → 0 (i.e., false) ! (exclamation) is the unary negation operator. A zero operand is converted to 1. A non-zero operand is converted to 0. Example: x = 0; y = 3; !x → 1 !y → 0

10 Increment and Decrement Operators Example: w = 0; z = 15; w++; → 1 ++w; → 2 z--; → 14 OperatorDescriptionExample (x is a variable) ++ Increment (add 1 to operand) ++x or x++ equivalent to x=x+1 -- Decrement (subtract 1 from operand) --x or x-- equivalent to x=x-1

11 Example: Prefix ( ++u, --u ) versus Postfix ( u++, u-- ) n = 5; x = ++n; Result: n → 6 x → 6 (Increment n, get value of n, store in x ) n = 5; x = n++; Result: n → 6 x → 5 (Get value of n, store in x, increment n )

12 Assignment Operators var op= expr is equivalent to var = var op expr where op is +, -, *, / Example: i = i + 2; can be replaced by i += 2; Assignment operators are: += -= *= /= Example: dec -= 2; is equivalent to dec = dec - 2; p *= 5; is equivalent to p = p * 5;

13 Type Conversion (Casting) “lower” type is promoted to “higher” type before the operation proceeds. The result is of the higher type.  If either operand is a long double, convert the other to long double  Otherwise, if either operand is double, convert the other to double  Otherwise, if either operand is float, convert the other to float  Otherwise, convert char and short to int  Then, if either operand is long, convert the other to long

14 The cast operator explicitly converts the type of an expression to a different type. Syntax: (type) n  Returns the value of n cast to the specified type.  The original type of n itself is not altered. Example: char x = 'A'; int y; y = x; // Automatic cast y = (int) x; // Explicit cast

15 Be aware of mixed types when doing arithmetic. Example: float x; int y = 3; x = 1 / 2; x = 1.0 / 2; x = y / 2; x = (float) y / 2; x contains 0.0 x contains 0.5 x contains 1.0 x contains 1.5

16 Memory Access Operators All variables are stored in memory, and each memory location has a unique address. The & operator returns the address of a variable. Example: Suppose x is located at memory address The 32-bit integer number 21 is stored there. OperatorDescriptionExample ( x is a variable) * Indirection *x & Reference (Address of) &x sizeof Size of type (in bytes) sizeof(x) Value of x is 21 Value of &x is 1024 sizeof(x) is 4 AddressContents x