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Programming Funamental slides1 Control Structures Topics to cover here: Introduction to Control Structures in the algorithmic language Sequencing Sequencing in C++ language

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Programming Funamental slides2 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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Programming Funamental slides3 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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Programming Funamental slides4 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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Programming Funamental slides5 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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Programming Funamental slides6 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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Programming Funamental slides7 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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Programming Funamental slides8 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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Programming Funamental slides9 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 3 + 6 OUTPUT x – y The semantics (execution) of this statement: 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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Programming Funamental slides10 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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Programming Funamental slides11 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 10 (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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Programming Funamental slides12 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. 1- 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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Programming Funamental slides13 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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Programming Funamental slides14 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

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Programming Funamental slides15 Examples on Simple Algorithms Example 1 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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Programming Funamental slides16 Example1.. cont. 1- Analysis stage: Problem Input: - num1 - num2 Problem Output: - summation of two numbers Formula: sum=num1+num2

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Programming Funamental slides17 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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Programming Funamental slides18 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 num2 sum 13 50 --- 63 The output: sum= 63

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Programming Funamental slides19 Flow Chart Input num1,num2 Sum = num1+ num2 Output sum

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Programming Funamental slides20 Examples on Simple Algorithms Example 2 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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Programming Funamental slides21 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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Programming Funamental slides22 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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Programming Funamental slides23 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 3 0.9 --- 2.7 The output: Total cost = 2.7

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Programming Funamental slides24 Flow Chart INPUT quantity, cost total_cost quantity * cost OUTPUT “Total cost

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Programming Funamental slides25 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 + n3 average = sum / 3

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Programming Funamental slides26 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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Programming Funamental slides27 Example 3.. cont. 3- Testing the algorithm n1 n2 n3 sum average 2 6 1 9 3 The output: average= 3 -----------------------------------------------------------

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Programming Funamental slides28 Flow Chart Input n1,n2,n3 sum = n1+n2+n3 Average = sum / 3 Output average

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Programming Funamental slides29 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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Programming Funamental slides30 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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Programming Funamental slides31 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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Programming Funamental slides32 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

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Programming Funamental slides33 2- The include compiler directive e.g. #include 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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Programming Funamental slides34 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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Programming Funamental slides35 3- Declaration Section Syntax: 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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Programming Funamental slides36 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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Programming Funamental slides37 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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Programming Funamental slides38 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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Programming Funamental slides39 3- The Assignment Statement in C++ Operator Precedence OperatorDescription !, +, - 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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Programming Funamental slides40 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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Programming Funamental slides41 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 void main() { int num1, num2, sum; cout >num1>>num2; sum = num1 + num2; cout<<"sum="<

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Programming Funamental slides42 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 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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Programming Funamental slides43 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 void main() { int n1, n2, n3; float s, average; cout >n1>>n2>>n3; s = n1 + n2 + n3; average = s / 3; cout<<"\n Average = \t"<

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Instructor - C. BoyleFall Semester - 2015

Instructor - C. BoyleFall Semester - 2015

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