review constructs

8/8/2019 Review Constructs

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DT211-2

ProgrammingRevision

Algorithms, Pseudocode Top-down

Refinementwith loopingRef Deitel & Deitel


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Pseudocode -Revision

Develop pseudocode algorithms for each of the following:Input two numbers and determine and display which (if either) is

the larger of the two numbers.Input the first number from the keyboard

Input the second number from the keyboard

if the first number is greater than the second numberPrint firstNumber

else

if the second number is greater than the first number

Print secondNumber

ElsePrint a message stating that the numbers are equal

endif

endif


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Pseudocode -Revision

Obtain a series of positive numbers from the keyboard,and determine and display the

sum of the numbers.

Assume that the user types the sentinel value -1 to

indicate end of data entry.Use the while statement.

sum=0

Input a value from the keyboard

While the input value is not equal to -1add the number to sum

input the next number

Print sum


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Pseudocode for Powers of 2

Write pseudocode that keeps printing themultiples (powers) of the integer 2, namely 2, 4,8, 16, 32, 64, and so on. The loop should notshould not terminate (i.e., you should create aninfinite loop). Implement this program andevaluate the outcome of execution.


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Pseudocode for Powers of 2

Allow program to run infinitelyOutput in form

n 2^n

1 22 4

3 8


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Code for Powers of 2


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Top-down Stepwise Refinement

This typically consists of three phases of pseudoceddevelopment.

Top-

a single statement that conveys the programs overall

function. First refinement-

divides the top task into smaller tasks into the general orderthat they must occur.

Second refinement- This identifies storage and variables and their initialisation. It

defines the control structures for managing the processinglogic including the termination and timing of any outputs.

More complex programs will require further refinements.


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Top-down Stepwise RefinementExample

Requirement spec: A class of students took aquiz. The grades (int 0 to 100) are available forinput on an input stream terminated by asentiner of -1. Determine the average grade for

the class.Top Refinement:

Determine the class average for the quiz

Second RefinementInitialize variablesInput, sum up and count the quiz gradesCalculate and print the class average


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Top-down Stepwise Refinement ExampleThird refinement:

Initialize total to zeroInitialize counter to zero

input the first grade (possibly the sentinel)While the user has not as yet entered the sentinel

Add this grade into the running totalAdd one to the grade counterInput the next grade (possibly the sentinel)

endwhile

if the counter is not equal to zeroSet the average to the total divided by the counterPrint the average

elsePrint No grades were entered

endif


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Stepwise RefinementSalesperson earnings

One large chemical company pays itssalespeople on a commission basis. Thesalespeople receive $200 per week plus 9% oftheir gross sales for that week. For example, asalesperson who sells $5000 worth ofchemicals in a week receives $200 plus 9% of$5000, or a total of $650. Develop a program

that will input each salespersons gross salesfor last week and will calculate and display thatsalesperson's earnings. Process onesalesperson's figures at a time.


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Salesperson earningsSample I/O dialogue

Enter sales in dollars (-1 to end): 5000.00Salary is: $650.00

Enter sales in dollars (-1 to end): 1234.56

Salary is: $311.11Enter sales in dollars (-1 to end): 1088.89

Salary is: $298.00

Enter sales in dollars (-1 to end): -1


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Salesperson earningsTop-down refinement

2)Top:For an arbitrary number of salespeople,

determine each salespersons earnings for the

last weekFirst refinement:

Input the salespersons sales for the week,

calculate and print the salespersons wagesfor the week,

then process the next salesperson


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Salesperson earningsTop-down refinement

Second refinement:

input the first salespersons sales in dollars

while the sentinel value (-1) has not been entered for the sales

calculate the salespersons wages for the week

print the salespersons wages for the week

input the next salespersons sales in dollars

endWhile


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Salesperson earnings code#include #include int main( void )

{float sales; /* gross weekly sales */float wage; /* commissioned earnings */

/* get first sales */printf( "Enter sales in dollars (-1 to end): " );

scanf( "%f", &sales );

/* loop until sentinel value read from user */while ( sales >= 0.0 ) {

wage = 200.0 + 0.09 * sales; /* calculate wage *//* display salary */

printf( "Salary is: $%.2f\n\n", wage );/* prompt for next sales */printf( "Enter sales in dollars (-1 to end): " );scanf( "%f", &sales );

} /* end while */getch();

return 0; /* indicate successful termination */


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Counter Controlled Looping withfor statement

The general format of the for statement is for ( expression1; expression2; expression3)

statement

where expression1 initializes the loop-control variable,

expression2 is the loop-continuation condition, andexpression3 increments the control variable.

In most cases, the for statement can be represented with

an equivalent while statement as follows:expression1;

while ( expression2 ) {

statement

expression3;}


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do while statement

In the while statement, the loop-continuationcondition is tested at the beginning of the loop

before the body of the loop is performed.

The dowhile statement tests the loop-continuation

condition afterthe loop body is performed.

Therefore, the loop body will be executed at least

once.


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do while statementUse dowhile statement to print the numbers from 1

to 10.The control variable counter is preincremented in theloop-continuation test.


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for ( expression1; expression2; expression3 ) statement

The three expressions in the for statement are optional.Ifexpression2 is omitted, C assumes that the condition is

true, thus creating an infinite loop.

One may omit expression1 if the control variable is

initialized elsewhere in the program.

expression3 may be omitted if the increment is calculated

by statements in the body of the for statement or if no

increment is needed.


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for ( expression1; expression2; expression3 )

statement

The increment express

ion in thefor s

tatement acts

like as

tand-alone C statement at the end of the body of the for.

The expressions

counter = counter + 1counter += 1

++counter

counter++

are all equivalent in the increment part of the for

statement.

preferred form iscounter++because the incrementing

occurs after the loop body is executed and seems more

natural.


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Notes on forfor ( expression1; expression2; expression3 ) statement

The initialization, loop-continuation condition andincrement can contain arithmetic expressions. For

example, when x = 2 and y = 10, the statementfor ( j = x; j


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for Examplesfor ( expression1; expression2; expression3 ) statement

The following examplesshow methods of varying the controlvariable in a for statement. Vary the control variable from 1 to 100 in increments of1.

for ( i = 1; i = 1; i-- )

Vary the control variable from 7 to 77 in steps of7.for ( i = 7; i = 2; i-= 2 )

Vary the control variable over the following sequence of values:2, 5, 8, 11,14, 17.for ( j = 2; j = 0; j -= 11 )


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For Examples Factorial n, n!

The factorial of a positive integern (written n! andpronounced n factorial) is equal to the product of thepositive integers from 1 to n.

N! = 1x2x3x..(n-1)xn

Develop a program that evaluates the factorials of theintegers from 1 to n and list them in tabular format.

n Factorial of n

1 1

2 23 6

4 24

5 120


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Top Print a table for factorial of the first n integersFirst refinement:

Input n,

display table column headerfor each number starting at 1 up to n,

calculate its factorial and display number and its

factorialendFor


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Second refinement:Declare variable n and counter x,

print k, tab, k!

for x=1 to ncalcualte k!

print k, k!

endFor


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Third refinement:Declare variable n and counter k,

print n, tab, n!

for k=1 to n

/* calculate x!

for j=1 to k

factorialK=factorialK * k

/* factorialK *= factorialKendfor

print k, factorialK!

endFor

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