Chapter 3 Branching Statements and
Program Design
•Introduction to Top-Down Design Techniques
•Use of Pseudocode
•The Logical Data Type
•Branches
•Additional Plotting Features
•More on Debugging MATLAB Programs
•Summary
•Exercises
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Chapter 3 Branching Statements and
Program Design
- Introduction to Top-Down Design Techniques
- Use of Pseudocode
- The Logical Data Type
- Branches
- Additional Plotting Features
- More on Debugging MATLAB Programs
- Summary
- Exercises
Introduction
- Sequential programs
- Reading input data, process it to produce a desired answer, print out the answer, and quit.
- There is no way to repeat sections of the program more than once
- There is no way to selectively execute only certain portion of the program depending on values of the input data.
- We will introduce a number of MATLAB statement
- Allow us to control the order in which statements are executed in a program. - Branches : select specific sections of the code to execute - Loops : which cause specific sections of the code to be repeated. (Chapter 4)
- We will introduce a top-down design techniques.
- We will introduce pseudocode algorithm.
Matlab Matlab
Top-Down Design
- Clearly state the problem that you are trying to solve.
(Page 88)
- Define the inputs required by the program and the outputs
to be produced by the program. (Page 89)
- Design the algorithm that you intend to implement in the
program. (Page 90)
- Algorithm: a step-by-step procedure for finding the solution to a problem.
- Stepwise refinement: pseudocode.
- Turn the algorithm into MATLAB statements.
- Test the resulting MATLAB program.
3.2 Use of Pseudocode
• Pseudocode is a hybrid mixture of
MATLAB and English.
• Pseudocode is intended to aid you in
organizing your thoughts before converting
them into MATLAB code.
– Example 2.3 (page 64)
– Pseudocode (page 93)
3.3 The Logical Data Type
• true or false
• MATLAB operators
– Relational operator
– Logic operator (single byte)
- Relational operators may be used to compare a scalar value with an array.
Relational operators can only compare two strings if they are
of equal lengths. (see chapter 6)
== symbol is a comparison operation that return a logical result
= symbol is a assignment operation
7 + 3 < 2 + 11 is equal to (7 + 3) < ( 2 + 11)
- A caution about the == and ~= operators
- For string comparison is safe
- For numeric is not safe
- Due to roundoff errors
- Logical ANDs: && and &
- Difference 1
- && supports short-circuit evaluations
- && will evaluate expression l1 and immediately return result
- if l1 is false , never evaluates l
- & evaluates both l1 and l2 before returning an answer
- Difference 2
- && works between scalar values
- & works with either scalar or array values, as long as the sizes of the arrays are compatible
- Difference 1
faster
x = a / b > 10.0 b = 0, x =? x = (b ~= 0) && (a/b > 10.0)
- Logical inclusive ORs: || and |
- Difference 1
- || supports partial evaluations
- || will evaluate expression l1 and immediately return result
- if l1 is true , never evaluates l
- | evaluates both l1 and l2 before returning an answer
- Difference 2
- || works between scalar values
- | works with either scalar or array values, as long as the sizes of the arrays are compatible
- Difference 1
- Using numeric data with logic operators
- Real numeric data can be use with logic operators
- ~5 is false, ~0 is true
- Logic operators may be used to compare scalar value with an array.
- Logic operators may be used to compare two arrays with same size
- Logic operators may not be used with complex or imaginary numeric data - 2i & 2i will produce an error when it is evaluated
- Real numeric data can be use with logic operators
- Hierarchy of operations
- All arithmetic operators are evaluated first in the order
previously described.
- All relational operators (==, ~=, >,>=,<,<=) are
evaluated, working from left to right.
- All ~ operators are evaluated.
- All & and && operators are evaluated, working from
left to right.
- All | and || , and xor operators are evaluated, working