Calling and defining a function

1. CTE 313
COMPUTER PROGRAMMING
LECTURE 3

2. LECTURE RECAP
Topics covered so far:
Lecture 1:
◦ Course Information & Introduction to Python Programming.
◦ Input, processing and Output
Lecture 2:
◦ Decision Making and Loop
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3. LECTURE 3
Topic to cover:
 Functions
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4. LECTURE OBJECTIVES
 To understand why programmers divide programs up into sets of
cooperating functions.
To be able to define new functions in Python.
To understand the details of function calls and parameter passing in
Python.
To write programs that use functions to reduce code duplication and
increase program modularity.
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5. Functions
The programs that we have written so far comprise a single function,
usually called main.
A function is a group of statements that exist within a program for the
purpose of performing a specific task.
Instead of writing a large program as one long sequence of statements, it
can be written as several small functions, each one performing a specific
part of the task.
These small functions can then be executed in the desired order to
perform the overall task.
A program that has been written with each task in its own function is
called a modularized program.
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6. Benefits of Modularizing a Program with Functions
Simpler Code
Code Reuse
Better Testing
Faster Development
Easier Facilitation of Teamwork
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7. Defining and Calling a Function
The code for creating a function is known as a function definition.
To execute the function, you write a statement that calls it.
The general format of a function definition in Python:
o def function_name():
o statement
o statement
o etc.
 The first line is known as the function header. It marks the beginning of the function
definition.
 The function header begins with the key word def, followed by the name of the function,
followed by a set of parentheses, followed by a colon.
 Beginning at the next line is a set of statements known as a block (a set of statements that
belong together as a group).
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8. A call to a function initiates a four step process:
 The calling program is suspended.
 The values of actual parameters are assigned to the formal parameters.
 The body of the function is executed.
 Control returns immediately following the function call in the calling program.
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9. Exercise 1:
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10. Exercise 2: More interesting…
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11. Local Variables
A local variable is created inside a function and cannot be
accessed by statements that are outside the function.
Different functions can have local variables with the same
names because the functions cannot see each other’s local
variables.
Anytime you assign a value to a variable inside a function, you
create a local variable.
The term local is meant to indicate that the variable can be
used only locally, within the function in which it is created.
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12. Exercise 3: Using Local Variable
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13. Passing Arguments to Functions
An argument is any piece of data that is passed into a function
when the function is called.
A parameter is a variable that receives an argument that is
passed into a function.
Sometimes it is useful not only to call a function, but also to
send one or more pieces of data into the function.
Pieces of data that are sent into a function are known as
arguments.
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14. Exercise 4: simple argument
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15. Exercise 5: Using argument for conversion
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16. Exercise 6: Passing Multiple Arguments
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17. QUESTIONS
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18. Assignment
1. There are three seating categories at a stadium. For a football game, Class A seats cost
N2000, Class B seats cost N1000, and Class C seats cost N500. Write a program that asks
how many tickets for each class of seats were sold, and then displays the amount of
income generated from ticket sales.
2. Write a program that calculates and displays a person’s body mass index (BMI). The BMI
is often used to determine whether a person is overweight or underweight for his or her
height. A person’s BMI is calculated with the following formula:
BMI = weight x 703 / height
where weight is measured in kg and height is measured in meters.
N.B: Use Function for each task.
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