Arithmetic Operators
Arithmetic Operations with
Variables
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Arithmetic Operators
Name
Operator
Addition
Subtraction
Multiplication
Division
Modulus
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+
*
/
%
Example
num1 + num2
initial - spent
fathoms * 6
sum / count
m%n
2
Modulus
%
The expression m % n yields the
remainder after m is divided by n.
 Modulus is an integer operation. - Both
operands MUST be integers.
 Examples : 17 % 5 = 2
6%3 = 0
9%2 = 1
5%8 = 5

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Integer Division
If both operands of a division
expression are integers, you will get an
integer answer. The fractional portion
is thrown away.
 Examples :
17 / 5 = 3
4 / 3 = 1
35 / 9 = 3
 Division where one operand is a floating
point number will produce a floating
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point answer.

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Division By Zero
Division by zero is mathematically
undefined.
 If you allow division by zero in a
program, it will cause a fatal error. your program will terminate immediately
and give an error message.
 Non-fatal errors will not cause program
termination, just produce incorrect
results.
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
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Uses of Modulus

Even and Odd
5 % 2 = 1 odd
4 % 2 = 0 even
Take the modulus by 2 of any integer, a
result of 1 means the number was odd,
a result of 0 means the number was
even.

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The Euclidean GCD algorithm
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Arithmetic Operators
Rules of Operator Precedence
Operator(s)
()
Precedence & Associativity
Evaluated first. If nested innermost first. If on same
level - left to right.
* / %
Evaluated second. If there are
several, evaluated left to right
+ -
Evaluated third. If there are
several, evaluated left to right.
=
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Evaluated last, right to left.
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Evaluation of expressions
a*b+c
Would multiply a * b first,
then add c to the result.
If we really want the sum of b and c to
be multiplied by a, use parentheses to
force the evaluation to be done in the
order we want.
a*(b+c)
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Practice With Evaluating Expressions
Given integer variables a, b, c, d, & e,
where a = 1, b = 2, c = 3, d = 4
Evaluate the following expressions :
a+b-c+d
a*b/c
1+a*b%c
a+d%b-c
e=d+c/b-a
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Good Programming Practices
The required C coding standards and
Indentation Styles are available on the
course homepage
 You will be expected to conform to
these standards for all programming
projects in this class.
 Pick one of the two indentation styles
shown and use it consistently.

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A Sample Project
We are going to write a
program in class that finds
the volume and surface
area of a box.
 Write the Algorithm
 Use the algorithm as a guide for writing
the code.

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Project :
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An algorithm for writing code
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Write the algorithm
Write the code using emacs
Try to compile the code
While there are still syntax errors
Fix errors
Try to compile the code
Test the program
Fix any semantic errors
Compile the code
Test the program
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