Department of Electronic & Electrical Engineering Expressions operators operands precedence associativity types.

Department of Electronic & Electrical Engineering Expressions An expression is comprises: variables constants function calls (must return a value) operators (unary or binary) operands

Department of Electronic & Electrical Engineering Example: 2.0*x*sin(z*y) constant variable another expression! function 2.0  *x  * ( z*y  sin ) order of evaluation

Department of Electronic & Electrical Engineering Arithmetic Operators Arithmetic operators + * - / can be used with any of the fundamental types ( int char float double ). % can only be used with integer types.

Department of Electronic & Electrical Engineering Pre/Post fix operators Increment / decrement a either before or after the value of the operand a = b++ ; assigns the a with the value of b then increments b. a = ++b ; increments the value of b then assigns the new value to a i++ ; /* increment i */

Department of Electronic & Electrical Engineering Precedence Expressions are usually evaluated from left to right (associativity) If an expression has different operators then precedence rules are applied Brackets can be used to form sub expressions (override precedence) For example arithmetic operators the * / and % operators will be evaluated before + or – e.g. 4+6/2 is equivalent to 4+ (6/2) (4-6)+2 4/6 - 2 (4/6)-2

Department of Electronic & Electrical Engineering Combining different types. Both operands the same type  results is the same. (2/3  0) integer and floating point type t  result will be floating point. e.g. 3.0/2 -> 1.5 When different sizes of the same type are used the result will be the type of the longest operand. These rules are applied to each step as an expression is evaluated e.g. 3/4*4.0 will give the result zero. ( because 3/4  0 ) For the above you could change the order of evaluation e.g. 4.0*3/4 When in doubt use brackets ! e.g. (4.0*3)/4 3/4*4.0 != 3/(4*4.0)

Department of Electronic & Electrical Engineering Examples 4* /8*34 x*y*func(4,5) 5%2 (78+84)*(34-45) int func(int a,int b) { return a*b-7; }

Department of Electronic & Electrical Engineering C and boolean variables (TRUE and FALSE) unlike some other languages C does not have a Boolean type. C uses int any non zero value is interpreted as TRUE. zero is interpreted as FALSE.

Department of Electronic & Electrical Engineering Relational (comparator) operators e.g. 5.0 > 4.0  1 for TRUE 6.0==7.0  0 for FALSE int result 1 or 0

Department of Electronic & Electrical Engineering Logical Operators (combining boolean values) 1 && 0  0 !( 1 || 0)  0 7 && 5  1

Department of Electronic & Electrical Engineering Logical examples. int x=5,y=6,z=7; /* we can declare and initialize at the same time ! */ int result; /* C does not have a boolean type. We use int */ result = x>y; /* result should be 0 which means FALSE */ result = x<y; /* result should be 1 which means TRUE */ result = (x > y) && ( ! z < x) ; /* Hmmm this is a bit tricky */ result = (x > y) && ( ! (z < x)) ; /* I think this is what I meant to write */

Department of Electronic & Electrical Engineering Operator Precedence Higher precedence at the top of the table

Department of Electronic & Electrical Engineering Associativity Consider the expression a ~ b ~ c. operator has left associativity, interpreted as (a ~ b) ~ c right associativity, interpreted as a ~ (b ~ c)

Department of Electronic & Electrical Engineering Associativity Consider If associativity is left to right this is (8-4)+2  6 right to left 8-(4+2)  2

Department of Electronic & Electrical Engineering Bitwise operators. Operates at the level of individual bits of a typebits

Department of Electronic & Electrical Engineering Examples : Bitwise operators int a=5; /* 101 */ int b=3; /* 011 */ int c; c= a & b ; /* bitwise AND c = 001 */ c= a | b; /* bitwise OR c = 111 */ c= a^b; /* XOR c = 110 */ c= ~a; /* complement c = */ c= a << 2 /* left shift by 2 c = */ c= a >> 2 /* right shift 2 c = 001 */

Department of Electronic & Electrical Engineering char x=2; /* */ char y=3; /* */ char z=x && y; /* result is 1 */ char w=x & y; /* result is 2 */ printf(" %d %d \n",z,w); bitwise versus logical operations