1. Relational Operations
Chapter 8
Arithmetic and
Relational Operations
Chapter 8: Arithmetic and Relational Operations

2. Assignment Statement Format: variable = expression;
variable is an identifier representing variable name
expression can be:
a variable [eg: min = num;]
a constant [eg: age = 20;]
a combination of the above
[eg: ave = (a1+a2+a3/count);]
Chapter 8
Assignment Statement

3. Assignment Statement Rules: lvalues appear on left of ‘=’
b = 50;
b = a + b;
lvalue
rvalue
Rules:
lvalues appear on left of ‘=’
rvalues appear on right of ‘=’
lvalues may be used as rvalues, but not vice versa
variable names are lvalues
constants and expressions are rvalues
Chapter 8
Assignment Statement

4. Assignment Statement Order of evaluation: right to left.
Example: a = z = 123;
123 is assigned to z
The assignment (z = 123) returns the value 123, which is assigned to a.
An assignment statement has a ‘value’. For example, ‘count = 12’; returns the value 12, besides assigning 12 to count.
Chapter 8
Assignment Statement

5. Assignment Statement
Assigning a value to a variable of different type?
int a, b; float x; char c;
a = 23.5;
x = 12;
c = 109;
b = 'n';
Chapter 8
Assignment Statement

6. Arithmetic Operators Sample program fah2cel.c. Spot the error.
Chapter 8
Arithmetic Operators

7. Unary Operators Unary plus +, unary minus -
Examples: +12, , -7.2e-3
Chapter 8
Unary Operators

8. Binary Operators Additon: 5 + 2 is 7; 5.4 + 2.7 is 8.1
Subtraction: is 3; is 2.7
Multiplication: 5 * 2 is 10; 3.2 * 1.5 is 4.8
Division: What is 5 / 2? 5.0 / 2.0? 0 / 25? / 0?
Modulus (only for integers): What is 5 % 2? 8 % 5? 15 % 5? 17 % -7? 15 % 0?
Chapter 8
Binary Operators

9. Data Types of Expressions
Same-type operands: result inherits the type.
7 + 3 is integer; is float
Mixed-type operands: result is of type that is more general.
is float; 5.0 / 2 is float
What is 5 / 2? 20 / 3?
Chapter 8
Data Types of Expressions

10. Data Types of Expressions
What values are stored in these variables?
float x, y;
int n;
x = 13 / 5;
y = 9 * 0.5;
n = 9 * 0.5;
Chapter 8
Data Types of Expressions

11. Promotion
In mixed-type expressions, the value of a more restricted type is automatically promoted to a more general type.
float x;
x = 13 / 5.0;
13 is promoted to float before division is carried out.
Chapter 8
Promotion

12. Cast
The cast operator (type) is used to explicitly change the type of the operand for the operation.
float x;
x = (float) 13 / 5;
What happens without the (float) cast?
Chapter 8
Cast

13. Precedence Rule
Precedence rule for arithmetic operators, from highest to lowest:
parentheses
Unary operators ++, --, +, -, (type)
Binary operators *, /, %
Binary operators +, -
Example: 3 * (12 - 7)
Chapter 8
Precedence Rule

14. Associativity Rule
For operators at the same precedence level, the associativity rule dictates the order of evaluation:
Unary operators: right to left
Binary operators: left to right
Example: 3 * (12 - 7) % 4 - (16 / (2 + 2 * 3 - 1))
Chapter 8
Associativity Rule

15. Compound Assignment Operators
For statement in this form:
variable = variable op expression;
we may write:
variable op= expression;
Examples:
c += 7; equivalent to c = c + 7;
d -= 4; d = d - 4;
e *= 5; e = e * 5;
f /= 3; f = f / 3;
g %= 9; g = g % 9;
Chapter 8
Compound Assignment Operators

16. Compound Assignment Operators
Is ‘j *= k + 1’ equivalent to
‘j = j * k + 1’ or ‘j = j * (k + 1)’?
What is the result of this?
(m + n) *= 2
Chapter 8
Compound Assignment Operators

17. Increment/Decrement Operators
++a or a++
equivalent to ‘a = a + 1’ or ‘a += 1’
--a or a--
equivalent to ‘a = a -1’ or ‘a -= 1’
Pre-increment (pre-decrement): Increment (decrement) variable, then use its value.
Post-increment (post-decrement): Use the variable’s value, then increment (decrement) it.
Chapter 8
Increment/Decrement Operators

18. Increment/Decrement Operators
Chapter 8
Increment/Decrement Operators

19. Increment/Decrement Operators
Avoid using the ++ and -- operators in complex expressions in which the variables they are applied appear more than once:
x = 5; i = 2;
y = i * x i;
is y assigned the value 13 or 18?
Chapter 8
Increment/Decrement Operators

20. Mathematical Functions
Mathematical functions are available in the math library. Some examples are:
pow(): to compute powers
fabs(): to return absolute values
sqrt(): to compute square roots
Need to include math.h file in your program, and compile with -lm option: cc -lm prog.c
Study the function prototypes in math.h.
Chapter 8
Mathematical Functions

21. Equality and Relational Operators
Selection and repetition constructs require the use of conditions.
if (condition) {
statements }
Conditions are formed by equality operator and relational operators.
Chapter 8
Equality and Relational Operators

22. Equality and Relational Operators
equal == x == y
not equal != x != y
greater than > x > y
less than < x < y
greater than or equal >= x >= y
less than or equal <= x <= y
if (x < y)
printf("%f is smaller than %f\n", x, y);
Chapter 8
Equality and Relational Operators

23. Equality and Relational Operators
Do not mix up == and =.
Zero -- false; non-zero values -- true.
if (123)
printf("Hello!\n");
if (7+3)
Chapter 8
Equality and Relational Operators

24. Equality and Relational Operators
False expression returns 0; true expression returns 1.
if (3 < 7)
printf("Hello!\n");
a = (123 > 321);
printf(”%d\n", a);
Chapter 8
Equality and Relational Operators

25. Equality and Relational Operators
Do not use == to compare equality of real numbers.
Real values may not be stored accurately.
if ((a/3)*3 == a)
printf("Hello!\n");
To test equality of 2 real numbers, test their difference instead (use fabs()), and take them as equal if the difference is small enough.
Chapter 8
Equality and Relational Operators

26. Logical Operators To combine conditions into more complex ones.
Logical AND: &&
Logical OR: ||
Logical NOT (negation): !
Evaluation from left to right.
Chapter 8
Logical Operators

27. Logical Operators Functions of logical operators.
What is the value of a?
int a;
a = (3 > 5) || (5 > 1);
Chapter 8
Logical Operators

28. Logical Operators Examples: if (grader == 1 && age >= 65)
++snrFemales;
if (semesterAvg >= 90 || finalExam >= 90)
grade = 'A';
if !(grade == 'F') /* or (grade != 'F') */
printf("Student passed.\n");
Chapter 8
Logical Operators

29. Logical Operators
Lazy (or short-circuit) evaluation of logical expressions: as soon as truth value can be determined, later expressions are skipped.
For logical AND, if front expression is false, the rest are skipped.
if (grader == 1 && age >= 65)
++snrFemales;
If (grader == 1) is false, there is no need to evaluate (age >= 65)
Chapter 8
Logical Operators

30. Logical Operators
For logical OR, if front expression is true, the rest are skipped.
if (semesterAvg >= 90 || finalExam >= 90)
grade = 'A';
if (semesterAvg >= 90) is true, there is no need to evaluate (finalExam >= 90).
Chapter 8
Logical Operators

31. Homework
Try exercises behind chapter 8.
Chapter 8
Homework