Transcript Control Structures

Control Structures
ELEC 206
Computer Applications for
Electrical Engineers
Dr. Ron Hayne
Structured Programming
 Algorithm Development
 Conditional Expressions
 Selection Statements
 Loops
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Structured Programming
 Sequence

Sequence of steps performed one after another
 Selection



Condition evaluated as true or false
if true, one set of statements executed
if false, another set of statements executed
 Repetition


Repeat (loop through) a set of steps
As long as a condition is true
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Flowchart Symbols
Operation
Symbol
Begin / End
start main
Input / Output
read radius
Computation
area = π*radius2
Comparison
is
radius < 0
?
no
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stop main
print radius, area
yes
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Sequence
start main
read radius
area = π*radius2
print radius, area
stop main
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Selection
read radius
is
radius < 0
?
no
yes
area = π*radius2
print error
print radius, area
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Repetition
time = 0
is
time  10
?
yes
no
compute velocity
print velocity
increment time
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Structured Programming
 Alternative Solutions


Readable
Not necessarily shortest
 Handle Error Conditions

Test for invalid data


Exit
Attempt to correct
 Generate Test Data


Cover different ranges of values
Test boundary conditions
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Debugging
 Compile Errors


Correct one or two obvious syntax errors
Recompile
 Execution Errors


Include cout statements
Provide memory snapshot of key objects
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Conditional Expressions
 Relational Operators






<
<=
>
>=
==
!=
 Logical Operators
less than
less than or equal to
greater than
greater than or equal to
equal to
not equal
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


&&
||
!
and
or
not
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Operator Precedence
Precedence
Operation
1
2
3
4
( )
++ -- +
* / %
+ -
5
6
7
< <= >
== !=
&&
8
9
||
= +=
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-=
-
!
(type)
>=
*=
/=
%=
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Examples
 a = 5.5
 b = 1.5
 k=3
 a + b >= 6.5
b - k > a
 a < 10 && a > 5
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Selection Statements
 if Statements
 if/else Statement
if (condition)
statement 1;
if (condition)
statement 1;
else
statement 2;
if (condition)
{
statement 1;
statement 2;
...
statement n;
}
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Example
read radius
is
radius < 0
?
no
yes
area = π*radius2
print error
print radius, area
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cin >> r;
if (r < 0)
cout << "error";
else
{
a = PI*r*r;
cout << r << a;
}
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Conditional Operator
 if/else Statement
if (a<b)
count++;
else
c = a + b;
 Conditional Statement
a<b ? count++ : c = a + b;
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Practice
 If dist is less than 50.0 and time is greater than 10.0,
then increment time by 2; otherwise, increment time
by 2.5.
if (dist < 50.0 && time > 10.0)
time+=2;
else
time+=2.5;
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Nested if/else Statements
if (code == 10)
cout << "Too hot - turn off." << endl;
else
if (code == 11)
cout << "Caution - recheck in 5 min." << endl;
else
if (code == 13)
cout << "Turn on fan." << endl;
else
cout << "Normal." << endl;
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Equivalent switch Statement
switch (code)
{
case 10:
cout << "Too hot - turn off." << endl;
break;
case 11:
cout << "Caution - recheck in 5 min." << endl;
break;
case 13:
cout << "Turn on fan." << endl;
break;
default:
cout << "Normal." << endl;
}
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Selection Statements
 switch Statement
switch (controlling expression)
{
case label_1:
statements;
case label_2:
statements;
...
default:
statements;
}
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Practice
 If rank equals 1 or
2 then print "Low",
else if rank equals
3 or 4 then print
"High", otherwise
print "Error".
switch (rank)
{
case 1:
case 2:
cout << "Low" << endl;
break;
case 3:
case 4:
cout << "High" << endl;
default:
cout << "Error" << endl;
}
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Loop Structures
 while Loop




Condition evaluated before statements are executed
If condition is false, statement block is skipped
If condition is true, statement block is executed and
condition is evaluated again
Beware of infinite loops

<Ctrl> C
while (condition)
{
statements;
}
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Example
/*-----------------------------------------------*/
/* Program chapter3_1
*/
/*
*/
/* This program prints a degree-to-radian table */
/* using a while loop structure.
*/
#include <iostream>
#include <iomanip>
using namespace std;
const double PI = 3.141593;
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Example
int main()
{
// Declare and initialize objects.
int degrees(0);
double radians;
// Set formats.
cout << fixed << setprecision(6);
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Example
// Print radians and degrees in a loop.
cout << "Degrees to Radians" << endl;
while (degrees <= 360)
{
radians = degrees*PI/180;
cout << setw(6) << degrees
<< setw(10) << radians << endl;
degrees += 30;
}
// Windows friendly exit
system("PAUSE");
return 0;
}
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Example
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Loop Structures
 do/while Loop


Condition tested at end of loop
Loop always executed at least once
do
{
statements
} while (condition);
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Example
// Print radians and degrees in a loop.
cout << "Degrees to Radians" << endl;
do
{
radians = degrees*PI/180;
cout << setw(6) << degrees
<< setw(10) << radians << endl;
degrees += 30;
} while (degrees <= 360);
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Loop Structures
 for Loop



Expression 1 initializes loop-control object
Expression 2 specifies condition to continue loop
Expression 3 specifies modification to loop-control object

After execution of statement block
for (exp_1; exp_2; exp_3)
{
statements;
}
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Example
// Print radians and degrees in a loop.
cout << "Degrees to Radians" << endl;
for (int degrees=0; degrees<=360; degrees+=30)
{
radians = degrees*PI/180;
cout << setw(6) << degrees
<< setw(10) << radians << endl;
}
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Practice
 What is the value of count after the nested for loops
are executed?
int count(0);
for (int k=-1; k<4; k++)
{
for (int j=3; j>0; j--)
{
count++;
}
}
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Loop Structures
 break Statement

Immediately exit from the loop
 continue Statement

Skip remaining statements in the current iteration
 Both useful when error conditions encountered
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Structured Input Loops
 Counter-controlled Loop

Number of data values is known
 Sentinel-controlled Loop

Special value indicates end of data
 End-of-data Loop


Continues while new data is available
End of file function (Ch 4)
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Counter-controlled Loop
// Prompt user for input.
cout << "Enter the number of exam scores ";
cin >> counter;
cout << "Enter " << counter << " exam scores
separated by whitespace ";
// Input exam scores using counter-controlled loop.
for(int i=1; i<=counter; i++)
{
cin >> exam_score;
sum = sum + exam_score;
}
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Counter-controlled Loop
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Sentinel-controlled Loop
input data_value
data_value
!=sentinel
False
True
input next
data_value
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Sentinel-controlled Loop
// Prompt user for input.
cout << "Enter exam scores separated by
whitespace." << endl;
cout << "Enter a negative value to indicate the
end of data. ";
// Input exam scores using sentinel-controlled loop.
cin >> exam_score;
while(exam_score >= 0)
{
sum = sum + exam_score;
count++;
cin >> exam_score;
}
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Sentinel-controlled Loop
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Problem Solving Applied
 Weather Balloons

Problem Statement


Using polynomials that represent altitude and velocity,
print a table using units of meters and meters per
second. Find the maximum altitude and its time.
Input/Output Description
Starting Time
Table of Velocities and Altitude
Time Increment
Maximum Altitude and its Time
Ending Time
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Problem Solving Applied

Hand Example
alt(t) = -0.12t4 + 12t3 - 380t2 + 4100t + 220
 v(t) = -0.48t3 + 36t2 - 760t + 4100


Starting Time
 t = 0 hours

Ending Time
 t = 5 hours

Time Increment
 1 hour
Time Altitude (m) Velocity (m/s)
0
1
2
3
220.00
3,951.88
6,994.08
9,414.28
1.14
0.94
0.76
0.59
4
5
11,277.28
12,645.00
0.45
0.32
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Problem Solving Applied

Algorithm Development
Get user input to specify times for table
 Generate and print conversion table
 Find and print maximum height and corresponding time

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Problem Solving Applied

Algorithm Refinement
Read initial, increment, final values from keyboard
 Set max_height and max_time to zero
 Print table heading and set time to initial
 While time is less than or equal to final
 Compute height and velocity
 Print height and velocity
 If height is greater than max_height
 Set new max_height and max_time
 Add increment to time
 Print max_time and max_height

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/*----------------------------------------------------*/
/* Program chapter3_7
*/
/*
*/
/* This program prints a table of height and
*/
/* velocity values for a weather balloon.
*/
#include <iostream>
#include <iomanip>
#include <cmath>
using namespace std;
int main()
{
// Declare and initialize objects.
double initial, increment, final, time, height,
velocity, max_time(0), max_height(0);
int loops;
// Get user input.
cout << "Enter initial value for table (in hours) \n";
cin >> initial;
cout << "Enter increment between lines (in hours) \n";
cin >> increment;
cout << "Enter final value for table (in hours) \n";
cin >> final;
// Print report heading.
cout << "\n\nWeather Balloon Information \n";
cout << "Time
Height
Velocity \n";
cout << "(hrs)
(meters) (meters/s) \n";
// Set formats.
cout << fixed << setprecision(2);
// Compute and print report information.
// Determine number of iterations required.
// Use integer index to avoid rounding error.
loops = (int)( (final - initial)/increment );
for (int count=0; count<=loops; count++)
{
time = initial + count*increment;
height = -0.12*pow(time,4) + 12*pow(time,3)
- 380*time*time + 4100*time + 220;
velocity = -0.48*pow(time,3) + 36*time*time
- 760*time + 4100;
cout << setw(6) << time << setw(10) << height
<< setw(10) << velocity/3600 << endl;
if (height > max_height)
{
max_height = height;
max_time = time;
}
}
// Print maximum height and corresponding time.
cout << "\nMaximum balloon height was " << setw(8)
<< max_height << " meters \n";
cout << "and it occurred at " << setw(6) << max_time
<< " hours \n";
Testing
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Summary
 Structured Programming




Algorithm Development
Conditional Expressions
Selection Statements
Loops
 Problem Solving Applied
 End of Chapter Summary



C++ Statements
Style Notes
Debugging Notes
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