Data Files ELEC 206 Computer Applications for Electrical Engineers Dr. Ron Hayne.

Data Files

ELEC 206

Computer Applications for Electrical Engineers

Dr. Ron Hayne

206_C4 2

Data Files

Defining File Streams Reading Data Files Generating a Data File Numerical Technique

Linear Regression

Problem Solving Applied

206_C4 3

File Stream Objects

File Stream Classes Derived from Stream Classes Input: ifstream Output: ofstream Header: fstream

Additional Member Functions open() fail() close()

206_C4 4

ifstream Class

ifstream Object ifstream sensor1;

File Association sensor1.open("sensor1.dat");

Define and Initialize ifstream sensor1("sensor1.dat");

Error Checking if( sensor1.fail() )

File Input sensor1 >> t >> motion;

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ofstream Class

ofstream Object ofstream balloon;

File Association balloon.open("balloon.dat");

Define and Initialize ofstream balloon("balloon.dat");

Append to Existing File balloon.open("balloon.dat", ios::app);

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ofstream Class

Prompt for Filename string filename; cout << "Enter output filename"; cin >> filename; balloon.open(filename.c_str());

File Output balloon << time << ' ' << height << ' ' << velocity/3600 << endl;

Close File balloon.close();

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Reading Data Files

Specified Number of Records Counter-controlled Loop

Trailer or Sentinel Signal Sentinel-controlled Loop

End of Data File End-of-file Loop

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Specified Number of Records

sensor1.dat10

0.0 132.5

0.1 147.2

0.2 148.3

0.3 157.3

0.4 163.2

0.5 158.2

0.6 169.3

0.7 148.2

0.8 137.6

0.9 135.9

sensor1.open(filename.c_str());

if(sensor1.fail())

{

cout << "Error";

}

else

{

sensor1 >> num_data_pts;

for (k=1; k<=num_data_pts; k++)

{

sensor1 >> time >> motion;

...

}

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Trailer or Sentinel Signals

sensor2.dat0.0 132.5

0.1 147.2

0.2 148.3

0.3 157.3

0.4 163.2

0.5 158.2

0.6 169.3

0.7 148.2

0.8 137.6

0.9 135.9

-99 -99


if(sensor2.fail())

{

cout << "Error";

}

else

{


do

{

...


} while (time >= 0);

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End-of-File

sensor3.dat0.0 132.5

0.1 147.2

0.2 148.3

0.3 157.3

0.4 163.2

0.5 158.2

0.6 169.3

0.7 148.2

0.8 137.6

0.9 135.9


if(sensor3.fail())

{

cout << "Error";

}

else

{


while ( !sensor3.eof() )

{

...


}

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Generating a Data File

...

#include <fstream>

#include <string>

...

int main()

{

...

string filename;

ofstream balloon;

...

// Prompt user for name of output file.

cout << "enter the name of the output file";

cin >> filename;

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Generating a Data File

// Open output file

balloon.open(filename.c_str());

// Set format flags for file output.

balloon << fixed << setprecision(2);

...

// Write data to file.

balloon << setw(6) << time << setw(10) << height

<< setw(10) << velocity/3600 << endl;

...

// Close file and exit program.

balloon.close();

return 0;

}

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Error Checkingint ivar1, ivar2;

cin >> ivar1 >> ivar2;

while(!cin.eof))

{

if(!cin)

{

cerr << "Error reading from standard input\n";

exit(1);

}

else

{

cout << ivar1 << ' ' << ivar2 << endl;

cin >> ivar1 >> ivar2;

}

}

206_C4 14

Linear Regression

Determine the linear equation that is the best fit to a set of data points Least-squares

Minimize sum of squared distances between line and data points

y = mx + b

22xnx

xynyxm

22

2

xnx

yxxyxb

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Ozone Measurements Problem Statement

Use least-squares technique to determine a linear model for estimating ozone mixing ratio at a specified altitude

Input/Output Description

Linear Model

Range of Altitudes

zone1.dat

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Hand ExampleAlt(km) Ratio(ppmv)zone1.dat

20 3

24 4

26 5

28 6

n = 4 Σx = 98 Σy = 18 Σxy = 454 Σx2 = 2436

m = 0.37 b = -4.6

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Algorithm DevelopmentRead data file valuesCompute sums and rangesCompute slope and y-intercept

206_C4 18


Algorithm RefinementSet count to zeroSet sumx, sumy, sumxy, sumx2 to zerowhile not at end-of-file

read x, y increment count if count = 1, then set first to x add x to sumx, y to sumy, xy to sumxy, x2 to sumx2

set last to xcompute m and bprint first, last, m, b

/*----------------------------------------------------*//* Program chapter4_6 *//* *//* This program computes a linear model for a set *//* of altitude and ozone mixing ratio values. */ #include<iostream>#include<iomanip>#include <fstream>#include <string>using namespace std;

int main(){ // Declare and initialize objects. int count(0); double x, y, first, last, sumx(0), sumy(0), sumx2(0), sumxy(0), denominator, m, b; string filename("zone1.dat"); ifstream zone1;

// Open input file. zone1.open(filename.c_str()); if(zone1.fail()) cerr << "Error opening input file\n"; else { // Read and accumulate information. zone1 >> x >> y; while ( !zone1.eof() ) { ++count; if (count == 1) first = x; sumx += x; sumy += y; sumx2 += x*x; sumxy += x*y; zone1 >> x >> y; } last = x;

// Compute slope and y-intercept. denominator = sumx*sumx - count*sumx2; m = (sumx*sumy - count*sumxy)/denominator; b = (sumx*sumxy - sumx2*sumy)/denominator;

// Set format flags cout << fixed << setprecision(2);

// Print summary information. cout << "Range of altitudes in km: \n"; cout << first << " to " << last << endl << endl; cout << "Linear model: \n"; cout << "ozone-mix-ratio = " << m << " * altitude + " << b << endl;

// Close file and exit program zone1.close(); } // end else system("PAUSE"); return 0;}

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Testing

206_C4 23

Summary

Defining File Streams Reading Data Files Generating a Data File Numerical Technique

Linear Regression

Problem Solving Applied End of Chapter Summary

C++ Statements Style Notes Debugging Notes

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Test #1 Review

Computer Hardware and Software Engineering Problem-Solving Methodology Program Structure Simple C++

Constants and Variables C++ Operators Standard Input and Output Basic Functions

206_C4 25

Test #1 Review

Structured Programming Algorithm Development Conditional Expressions Selection Statements Loops

Data Files Defining File Streams Reading Data Files Generating Data Files

Data Files ELEC 206 Computer Applications for Electrical Engineers Dr. Ron Hayne.

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