Modular Programming

ELEC 206

Computer Applications for Electrical Engineers

Dr. Ron Hayne

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Outline

Modularity Programmer Defined Functions Parameter Passing Storage Class and Scope

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Modularity

Modules Can be written and tested separately Testing is easier (smaller) Doesn't need to be retested Reduces length of program Hides details (abstraction)

Structure Charts Module structure of a program (not sequence)

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Programmer-Defined Functions

Function Definition Function Header Parameter Declarations Function Body Return Statement

return_type function_name(parameter declarations)

{

declarations;

statements;

}

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Example Function

/* This function converts degrees Celsius */

/* to degrees Fahrenheit. */

double Celsius_to_Fahr(double Celsius)

{

// Declare objects.

double temp;

// Convert.

temp = (9.0/5.0)*Celsius + 32;

return temp;

}

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Program Using a Function

/* Program chapter5_2 */

/* */

/* This program prints 21 values of the sinc */

/* function in the interval [a,b] using a */

/* programmer-defined function. */

#include <iostream>

#include <cmath>

using namespace std;

//Function Prototype

double sinc(double x);

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Program Using a Function

int main()

{

...

// Compute and print table of sinc(x) values.

cout << "x and sinc(x) \n";

for (int k=0; k<=20; k++)

{

new_x = a + k*x_incr;

cout << new_x << " " << sinc(new_x) << endl;

}

// Exit program.

return 0;

}

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Program Using a Function

/* This function evaluates the sinc function. */

double sinc(double x)

{

if (abs(x) < 0.0001)

return 1.0;

else

return sin(x)/x;

}

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Parameter Passing

Call by Value Value of the function argument passed to the

formal parameter of the function

Call by Reference Address of the function argument passed to the

formal parameter of the function

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Call by Value Example

/* Incorrect function to switch two values */

void switch(int a, int b)

{

int hold;

hold = a;

a = b;

b = hold;

return;

}

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Call by Reference Example

/* Correct function to switch two values */

void switch2(int& a, int& b)

{

int hold;

hold = a;

a = b;

b = hold;

return;

}

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Storage Class and Scope

Local Objects Defined within a function Can be accessed only within the function Automatic storage class (default) Static storage class (retained entire execution)

Global Objects Defined outside all functions Can be accessed by any function External storage class

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Global/Local Example

int count(0);

...

int main()

{

int x, y, z;

...

}

int calc(int a, int b)

{

int x;

count += x;

...

}

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Summary

Modularity Programmer Defined Functions Parameter Passing Storage Class and Scope

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Random Numbers

cstdlib int rand();

Generates integer between 0 and RAND_MAX void srand(unsigned int);

Specifies the seed for the random number generator

Generating random integers over a specified range (a, b) Modulus operator (%)

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Example

/* This program generates and prints ten random */

/* integers between user-specified limits. */

#include <cstdlib>

#include <iostream>

using namespace std;

// Function prototype.

int rand_int(int a, int b);

int main()

{

...

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Example

srand(seed);

...

// Generate and print ten random numbers.

cout << "Random Numbers: \n";

for (int k=1; k<=10; k++)

{

cout << rand_int(a,b) << ' ';

}

cout << endl;

// Exit program.

return 0;

}

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Example

/* This function generates a random integer */

/* between specified limits a and b (a<b). */

int rand_int(int a, int b)

{

return rand()%(b-a+1) + a;

}

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Problem Solving Applied

Instrumentation Reliability Problem Statement

Compare the analytical and simulation reliabilities for a series configuration with three components and for a parallel configuration with three components.

Input/Output Description

Component reliabilityAnalytical reliability

Number of trials

Random seedSimulation reliability

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Problem Solving Applied

Hand ExampleAnalytical Reliability

r = 0.8

Series Configuration r_series = r3 = 0.512

Parallel Configuration r_parallel = 3r - 3r2 + r3 = 0.992

Comp Comp Comp

Comp

Comp

Comp

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Problem Solving Applied

Hand ExampleSimulation Reliability (3 random trials)

0.939775 0.0422243 0.929037 0.817733 0.211689 0.9909 0.0377037 0.103508 0.407272

Series Configuration All must be less than or equal to 0.8 One success = 0.333333

Parallel Configuration Any must be less than or equal to 0.8 Three successes = 1.0

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Problem Solving Applied

Algorithm DevelopmentRead component reliability, number of trials, seedCompute analytical reliabilitiesWhile k <= number of trials

Generate three random numbers between 0 and 1 If each number <= component reliability

Increment series_success If any number <= component reliability

Increment parallel_success Increment k

Print analytical reliabilitiesPrint simulation reliabilities

/* This program estimates the reliability *//* of a series and a parallel configuration *//* using a computer simulation. */

#include <iostream>#include <cstdlib>#include <cmath>using namespace std;

// Function prototypes double rand_float(double a, double b);

int main(){ // Declare objects. unsigned int seed; int n; double component_reliability, a_series, a_parallel, series_success=0, parallel_success=0, num1, num2, num3;

// Get information for the simulation. cout << "Enter individual component reliability: \n"; cin >> component_reliability; cout << "Enter number of trials: \n"; cin >> n; cout << "Enter unsigned integer seed: \n"; cin >> seed; srand(seed); cout << endl;

// Compute analytical reliabilities. a_series = pow(component_reliability,3); a_parallel = 3*component_reliability - 3*pow(component_reliability,2) + pow(component_reliability,3);

// Determine simulation reliability estimates. for (int k=1; k<=n; k++) { num1 = rand_float(0,1); num2 = rand_float(0,1); num3 = rand_float(0,1); if (((num1<=component_reliability) && (num2<=component_reliability)) && (num3<=component_reliability)) { series_success++; } if (((num1<=component_reliability) || (num2<=component_reliability)) || (num3<=component_reliability)) { parallel_success++; } }

// Print results. cout << "Analytical Reliability \n"; cout << "Series: " << a_series << " " << "Parallel: " << a_parallel << endl; cout << "Simulation Reliability " << n << " trials\n"; cout << "Series: " << (double)series_success/n << " Parallel: " << (double)parallel_success/n << endl;

// Exit program. return 0;}/*----------------------------------------------------*//* This function generates a random *//* double value between a and b. */

double rand_float(double a, double b){ return ((double)rand()/RAND_MAX)*(b-a) + a;}/*----------------------------------------------------*/

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Testing

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Testing

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Summary

Modularity Programmer Defined Functions Parameter Passing Storage Class and Scope Random Numbers Problem Solving Applied End of Chapter Summary

C++ Statements Style Notes Debugging Notes