Chapter 8
Arithmetic and
Relational Operations
Chapter 8: Arithmetic and
Relational Operations
1
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
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Assignment Statement
a = 40;
b = 50;
lvalue
rvalue
b = a + b;
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
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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
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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
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Arithmetic Operators
Sample
program
fah2cel.c.
Spot the
error.
/* Converts degrees Fahrenheit to degrees Celsius
* Author: Garfield
Date: 25 July 1997
* Note: This program contains a subtle error too!
*/
#include <stdio.h>
int main (void)
{
float fah,
/* degrees in Fahrenheit */
cel;
/* degrees in Celsius */
printf ("Enter degrees in Fahrenheit: ");
scanf ("%f", &fah);
cel = 5/9 * (fah - 32);
printf ("That equals %f degrees in Celsius.\n\n",
cel);
return 0;
}
Chapter 8
Arithmetic Operators
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Unary Operators
Unary plus +, unary minus Examples: +12, -45.80, -7.2e-3
Chapter 8
Unary Operators
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Binary Operators
Additon: 5 + 2 is 7; 5.4 + 2.7 is 8.1
Subtraction: 5 - 2 is 3; 5.0 - 2.3 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?
19 / 0?
Modulus (only for integers): What is 5 % 2?
8 % 5? 15 % 5? 17 % -7? 15 % 0?
Chapter 8
Binary Operators
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Data Types of Expressions
Same-type operands: result inherits the type.
7 + 3 is integer; 2.3 + 4.56 is float
Mixed-type operands: result is of type that is
more general.
7 + 3.0 is float; 5.0 / 2 is float
What is 5 / 2? 20 / 3?
Chapter 8
Data Types of Expressions
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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
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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
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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
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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
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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
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Compound Assignment Operators
For statement in this form:
variable = variable op expression;
we may write:
variable op= expression;
Examples:
 c += 7;
 d -= 4;
 e *= 5;
 f /= 3;
 g %= 9;
Chapter 8
equivalent to
c = c + 7;
d = d - 4;
e = e * 5;
f = f / 3;
g = g % 9;
Compound Assignment Operators
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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
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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
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Increment/Decrement Operators
/* Pre-incrementing and post-incrementing */
#include <stdio.h>
int main(void)
{
int c;
c = 9;
printf("%d\n", c);
printf("%d\n", c++);
printf("%d\n\n", c);
c = 9;
printf("%d\n", c);
printf("%d\n", ++c);
printf("%d\n", c);
return 0;
/* post-increment */
9
9
10
9
10
10
/* pre-increment */
/* successful termination */
}
Chapter 8
Increment/Decrement Operators
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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
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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
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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
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Equality and Relational Operators
Operators:
 equal ==
 not equal !=
 greater than >
 less than <
 greater than or equal >=
 less than or equal <=
x == y
x != y
x>y
x<y
x >= y
x <= y
if (x < y)
printf("%f is smaller than %f\n", x, y);
Chapter 8
Equality and Relational Operators
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Equality and Relational Operators
Do not mix up == and =.
Zero -- false; non-zero values -- true.
if (123)
printf("Hello!\n");
if (7+3)
printf("Hello!\n");
Chapter 8
Equality and Relational Operators
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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
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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
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Logical Operators
To combine conditions into more complex ones.
Logical operators:
 Logical AND: &&
 Logical OR: ||
 Logical NOT (negation): !
Evaluation from left to right.
Chapter 8
Logical Operators
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Logical Operators
Functions of logical operators.
expr1
expr2
expr1 && expr2
expr1 || expr2
! expr1
0
0
nonzero
nonzero
0
nonzero
0
nonzero
0
0
0
1
0
1
1
1
1
1
0
0
What is the value of a?
int a;
a = (3 > 5) || (5 > 1);
Chapter 8
Logical Operators
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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
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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
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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
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Homework
Try exercises behind chapter 8.
Chapter 8
Homework
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