Objective-C Fundamentals

296 APPENDIX B The basics of C
You may like to get into the habit of prefixing your own publicly visible identifiers
with a prefix of your own choosing, perhaps based on the initials of your name
or company.
With the proper naming of variables and other elements out of the way and no
longer producing compile-time errors, let’s explore how to use one or more variables
to calculate new values or to answer questions.
B.2 Expressions
It’s uncommon for an application to be developed without requiring at least one mathematical
calculation, so C provides a rich set of operators for mathematical expressions.
B.2.1
Arithmetic operators
The most obvious operators are the arithmetic ones that perform the basic mathematical
operations we’re all familiar with. These operators are listed in table B.2.
Table B.2
Arithmetic operators available in C
Operator
Description
+ Addition
- Subtraction
* Multiplication
/ Division
% Modulus (remainder)
These arithmetic operators all have their expected behavior. For example, the expression
4 + 3 results in the value 7 being calculated. The modulus operator returns the
remainder of an integer division operation, so 9 % 2 equals 1 because 2 goes into 9
four times with 1 left over.
B.2.2
Comparison operators
Once you’ve calculated one value, you may want to compare it against another. Relational
operators allow this comparison, which results in a Boolean value being calculated
that indicates the truth of the statement. Table B.3 outlines the available
relational operators.
As an example, the expression x >= 5 * 10 determines if the value of variable x is
greater than or equal to 50 (the value of the expression on the right side of the >=
operator).
Sometimes comparing a single value isn’t enough. For example, you may want to
check if a person’s age is greater than 25 years and weight is less than 180 pounds. In
such scenarios, you must use compound conditional statements.