1. Computer Science 2

2. Learning Objectives
Review how to dry run a program that uses procedures
Understand how read a program that uses functions.
Understand the three parts of a function.
Be able to write a program that uses functions.

3. Today’s Overview Review of procedures Introduce Functions
Start to code

4. Remember boxes and arrows.
program confusion7;
var
w,x,y,z:integer;
procedure see1(var n, z:integer; w:integer);
y:integer;
begin
writeln(w:5, n:5, y:5, z:5);
y:=4;
n:= w mod x;
z:= w div y;
w:= 3 * y;
end;
procedure see2( n, z:integer; var w:integer);
y:= 5;
Remember boxes and arrows.
begin
x:=10;
y:=9;
z:=8;
w:=7;
writeln(w:5, x:5, y:5, z:5);
see1(x, w, y);
see2(y, w, x);
end.

5. What do you think this program does?
Program ProcedureFunctionExample;
{************************************}
procedure getTheNumbers(var first, second:integer);
begin
writeln(‘Please enter a number’);
readln(first);
writeln(‘Please enter another number’);
readln(second);
end;
{***************************************}
function findTheTotal(beginning, ending : integer):integer;
writeln(‘Now in the FindTheTotal function’);
findTheTotal:=beginning + ending;
{*****************************************}
var
num1,num2,tot:integer;
begin {Of the main body}
getTheNumbers(num1, num2);
tot:=findTheTotal(num1, num2);
writeln(‘The total of ‘,num1,’ + ‘, num2, ‘ = ‘, tot);
readln;
end. {Of the main body}

6. Functions Like a procedure, but the call statement represents a value.
When do you use one?
When you want to return one value.
Calculate the average of a bunch of numbers
Fancy Boolean expression.

7. Three parts of the function
The call statement
The header
The code

8. What is different than the procedure’s call statement?
The call statement
tot:=findTheTotal(num1, num2);
In General
answer:=functionname(Arguments);
If there are no arguments
answer:= functionname;
What is different than the procedure’s call statement?

9. Getting Fancy with Calls Statements
Use order of operations
Calling a function in a writeln Writeln(findTheTotal(num1, num2), ‘ is the answer’); Calling a function in a condition If (findTheTotal(num1,num2) < 20) then Calling a function in a function call Total:= findTheTotal(num1, findTheTotal(num3, num4));

10. The Header ReturnType can be any simple data type:
function FindTheTotal(beginning, ending : integer):integer;
In General
function Functionname(Parameters):ReturnType;
ReturnType can be any simple data type:
Integer, real, string, boolean, char,

11. The Code {***************************************}
Can have local: const, type and var
{***************************************}
function FindTheTotal(beginning, ending : integer):integer;
begin
writeln(‘Now in the FindTheTotal function’);
FindTheTotal:=beginning + ending;
end;
{*****************************************}
This line of code gives the value to the function

12. Reading a program. begin a:= 6; b:= 12; writeln(a:4,b:4);
program funInFunction;
var
a,b:integer;
function one(a,b:integer):integer;
c:integer;
begin
c:= a+2*b;
one:= c DIV 2;
end;
function two:integer;
first, second:integer;
first:= 15;
second:= 10;
two:= first - second;
Reading a program.
begin
a:= 6;
b:= 12;
writeln(a:4,b:4);
a:= one(b,a);
writeln(two:4);
b:= one(a,b) + two - 6;
writeln(a:4,b:4 );
end.

13. Review What is a function? When do you use a function?
Where do functions go in the code?

14. Functions Program #1
Write a function to convert from Radians to degrees
Convert from Fahrenheit to Celsius
Sent the radius and height and calculate the volume of a cylinder.

15. Function #2 Program Options
Sent nothing, but inside the functions gets 10 scores and calculates and returns the average
Factorial Function
Input: Any positive integer;
Output: The factorial of the number
Example: Input: 5
Output: 5! = 120
Create the header and call statement for one.