1. Programming Funamental slides
Control Structures
Topics to cover here:
Introduction to Control Structures in the algorithmic language
Sequencing
Sequencing in C++ language
Programming Funamental slides

2. Programming Funamental slides
Control Structures
In your algorithm (or program), you can use different types of statements.
There are 3 categories of control structures:
1- Sequencing
2- Selection
3- Repetition
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3. Programming Funamental slides
1- Sequencing
A compound statement (or a block) is a sequence of statements ordered in a way to give a solution: e.g. S1 S2 S3
is a sequence of 3 statements
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4. INPUT/OUPUT statements
1- Sequencing (Cont.)
The statements that have a sequential control:
1- INPUT/OUPUT statements
2- Assignment statement
INPUT/OUPUT statements
INPUT statement (in pseudo code):
Use Input statement to input data into variables from the standard input device (e.g. a keyboard).
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5. Programming Funamental slides
INPUT Statement
Syntax: INPUT List of variables
where, List of variables contains one or more variables
e.g INPUT x
INPUT a, b
The semantics (execution) of this statement:
You can enter the values you want for the variables in the statement from the keyboard and the computer will assign these values into the variables (stores them in memory).
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6. OUPUT Statement (in pseudo code)
The OUTPUT statement has many uses.
Use OUTPUT statement to output
- The values of variables stored in memory.
A message (i.e. a string of characters).
The value of an expression.
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7. OUPUT Statement (in pseudo code).. cont.
Syntax:
1- OUTPUT List of variables
where, List of variables contains one or more variables
e.g. OUTPUT x
OUTPUT a, b
The semantics (execution) of this statement:
This statement allows the computer to access the locations of the variables mentioned in the statement and displays their contents on an output device (e.g. a screen).
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8. OUPUT Statement (in pseudo code).. cont.
2- OUTPUT message
where message may by any string of
characters enclosed with double quotas.
e.g. OUTPUT “Enter 3 values”
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9. OUPUT Statement (in pseudo code) (Cont.)
The semantics (execution) of this statement:
This statement will display the message on the screen.
3- OUTPUT expression
where expression is any arithmetic expression
e.g. OUTPUT
OUTPUT x – y
First, the expression is evaluated, then the result will be displayed on the screen. For the first example, it will display 9.
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10. OUPUT Statement (in pseudo code).. cont.
NOTE
You can mix between the different types of the OUTPUT statements.
e.g.
OUTPUT “Length = “ , length
The semantics (execution) of this statement:
This statement will display the message
Length = on the screen and on the same line it will display the value of the variable length.
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11. Assignment Statement (in pseudo code)
Storing a new value in a memory location is called assignment.
We use the operator  as assignment operator.
Syntax:
Variable  Expression
The semantics (execution) of this statement:
1- The Expression on the right of  is evaluated
2- The result of the expression is assigned to the variable on the left of  .
e.g.
X  (This means that X has 10 now )
Y  X + 5 (This means that Y has 11 now, if X is 6)
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12. Assignment Statement (Cont.)
NOTE:
The right hand side (RHS) of the assignment statement should be of the same data type of the left hand side (LHS).
e.g.
T  true
This will be correct if T is of Boolean type.
2- A  x + y * 2
This will be correct if A has a numeric data type (e.g. integer, or real) and the value of the expression on (RHS) has the same numeric data type.
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13. Assignment Statement (Cont.)
How to execute a statement like X  X + 1 ?
Suppose we have:
X  5
Then to execute X  X + 1, we proceed as follows:
X X  5
X  X + 1 5 6
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14. Assignment Statement .. cont.
Dereferencing:
If we want to copy a value from one memory location (say, X) into another location (say, Y), we say that we dereference a variable.
e.g.
X  5
Y  10
X  Y // now X has the value 10
X Y 10 5 10
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15. Examples on Simple Algorithms
Write an algorithm to Compute and print the summation of two numbers.
First, we have to analyze the problem to understand what is the input, output of the problem, and which formula to use to solve the problem (if any).
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16. Programming Funamental slides
Example1 .. cont.
1- Analysis stage:
Problem Input:
- num1
- num2
Problem Output:
- summation of two numbers
Formula:
sum=num1+num2
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17. Programming Funamental slides
Example1 .. cont.
2- Algorithm Design
We write the algorithm by using the pseudo code
ALGORITHM Summation INPUT num1, num2 sum num1+ num2 OUTPUT “sum=“ ,sum END Summation
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18. Programming Funamental slides
Example1 .. cont.
3- Testing the algorithm
We give a sample data to see whether the algorithm solves the problem correctly or not.
To give a sample data, proceed as follows:
1- Prepare a table to contain all variables of the algorithm.
2- Give any data you like as input.
3- Calculate any formula in the algorithm using these data.
4- Show the output
e.g.
num1 num sum 63
The output:
sum= 63
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19. Programming Funamental slides
Flow Chart
Input num1,num2
Sum = num1+ num2
Output sum
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20. Examples on Simple Algorithms
Write an algorithm to determine the total cost of apples given the number of kilos of apples purchased and the cost per kilo of apples.
First, we have to analyze the problem to understand what is the input, output of the problem, and which formula to use to solve the problem (if any).
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21. Programming Funamental slides
Example2 .. cont.
1- Analysis stage:
Problem Input:
- Quantity of apples purchased (in kilos)
- Cost per kilo of apples (in dinar/fils per kilo)
Problem Output:
- Total cost of apples (in dinar/fils)
Formula:
Total cost = Number of kilos of apples × Cost per kilo
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22. Programming Funamental slides
Example2 .. cont.
2- Algorithm Design
We write the algorithm by using the pseudo code
ALGORITHM apples
INPUT quantity, cost
total_cost  quantity * cost
OUTPUT “Total cost = “ , total_cost
END apples
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23. Programming Funamental slides
Example2 .. cont.
3- Testing the algorithm
We give a sample data to see whether the algorithm solves the problem correctly or not.
To give a sample data, proceed as follows:
1- Prepare a table to contain all variables of the algorithm.
2- Give any data you like as input.
3- Calculate any formula in the algorithm using these data.
4- Show the output
e.g.
quantity cost total_cost
2.7
The output:
Total cost = 2.7
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24. Programming Funamental slides
Flow Chart
INPUT quantity, cost
total_cost  quantity * cost
OUTPUT “Total cost
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25. Programming Funamental slides
Example 3
The problem statement:
Write an algorithm that Compute and print the average of three numbers
1- Analysis stage:
Problem Input:
- n1,n2,n3
Problem Output:
- average
Formula:
sum= n1 + n2 + n average = sum / 3
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26. Programming Funamental slides
Example 3 .. cont.
2- Algorithm Design
ALGORITHM Avg INPUT n1, n2, n3 sum n1 + n2 + n3 average  sum / 3 OUTPUT average END Avg
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27. Programming Funamental slides
Example 3 .. cont.
3- Testing the algorithm
n n n sum average 9 3
The output:
average= 3
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28. Programming Funamental slides
Flow Chart
Input n1,n2,n3
sum = n1+n2+n3
Average = sum / 3
Output average
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29. Coding (Writing a Program)
After testing your algorithm, you can code it in any programming language.
In our lab, we are going to use C++ language.
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30. Programming Funamental slides
C++ Language Elements
The general form of a C++ program
// File: filename
// Program description
# include compiler directives
void main ( ) //main function of the program {
declarations section
executable statement section }
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31. Programming Funamental slides
1- Comments in Programs
In C++, the two symbols // are used to denote a program comment.
If comments need more than one line, then you can use the symbols /* to begin comment and */ to end it.
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32. 2- The include compiler directive
The line begins with #include represents a compiler directive.
A compiler directive is processed at compilation time.
C++ syntax:
# include <filename>
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33. 2- The include compiler directive
e.g.
#include <iostream.h>
iostream.h is the name of a C++ library header file whose contents are inserted in place of the #include line during compilation.
iostream.h is used to manipulate input/output operations
The standard I/O stream objects, cin and cout are already defined in iostream.h
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34. Programming Funamental slides
3- Declaration Section
The declaration section tells the compiler what data are needed in the program.
Declarations are based on the problem data requirements identified during the problem analysis.
All identifiers must be declared before they are used.
Every identifier associated with a problem data element must be declared only once in the declaration section.
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35. Programming Funamental slides
3- Declaration Section
Syntax: <type> List-of-identifiers
where, type is any predefined type in C++, and
List-of-identifiers is a list that contains one or more identifiers.
1- Declaring identifiers of integer type :
int x ;
int x, y;
2- Declaring identifiers of character type:
char c1, c2 ;
3- Declaring identifiers to hold real numbers:
float sum ;
double total ;
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36. 4- Executable Statements Section
Execution statements cause some kind of action to occur when a program is executed.
We have seen three executable statements in the algorithmic language: INPUT, OUTPUT, and assignment statements.
1- The Input statement in C++
Syntax: cin >> identifier >> identifier ;
This will cause any data value, typed by the user from the standard input devise (usually the keyboard), to be read into the identifiers mentioned in the statement.
e.g. cin >> length ;
cin >> x >> y ;
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37. 2- The Output Statement in C++
1- Syntax: cout << identifier << identifier ;
This statement causes the values of the identifiers to be displayed to the standard output device (e.g. a screen).
e.g cout << length ;
2- Syntax: cout << “any message” ;
This statement causes the message between quotation to be displayed to the standard output device.
e.g. cout << “ Enter three integer values “ ;
3- Syntax: cout << endl ;
This statement causes a new line to be displayed in the output. Use this for output clarity.
Note: You can mix between all type of cout.
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38. 3- The Assignment Statement in C++
Syntax: variable = Expression ;
This statement causes the value of Expression to be assigned into the variable on the LHS of the assignment statement.
e.g.
x = y ;
z = t * 2 ;
w = 6 ;
w = w + 1 ;
NOTE:
Expression has the same operations with the same precedence rules as with the algorithmic language with some different symbols.
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39. 3- The Assignment Statement in C++
Operator Precedence
Operator Description
! , + , not, unary plus, unary minus
* , / , % multiplication, division, mod
binary plus, binary minus
<, <= ,>, >= less than, less or equal, greater
than, greater or equal
== , != equal, not equal
&& and
|| or
= assignment
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40. Examples on C++ Programs
Now, we will code the previous examples given in the algorithmic language into C++ language.
In the lab, we will use Visual C++ environment.
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41. Examples on C++ Programs
Example 1: (refer to the algorithm of Example 1 on slide number 17)
/*This program Compute and print the summation of two numbers */
#include <iostream.h> void main() { int num1, num2, sum; cout<<"Please Enter two numbers:"; cin>>num1>>num2; sum = num1 + num2; cout<<"sum="<<sum<<endl; }
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42. Examples on C++ Programs
Example 2: (refer to the algorithm of Example 1 on slide number 17)
// File: apples.cpp
/*This program calculates the price of purchasing some kilos of apples */
#include <iostream.h>
void main ( )
{ int quantity ;
float cost , total_cost ;
cin >> quantity >> cost ;
total_cost = quantity * cost ;
cout << “Total cost = “ << total_cost << endl ; }
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43. Examples on C++ Programs
Example 3: (refer to the algorithm of Example 1 on slide number 17)
/*This program Compute and print the average of three numbers */
#include <iostream.h> void main() { int n1, n2, n3; float s, average; cout<<"Please Enter three integers"; cin>>n1>>n2>>n3; s = n1 + n2 + n3; average = s / 3; cout<<"\n Average = \t"<<average<<endl; }
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