Modular Programming ELEC 206 Computer Applications for Electrical Engineers Dr. Ron Hayne

206_C52 Outline  Modularity  Programmer Defined Functions  Parameter Passing  Storage Class and Scope

206_C53 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)

206_C54 Programmer-Defined Functions  Function Definition Function Header Parameter Declarations Function Body Return Statement return_type function_name(parameter declarations) { declarations; statements; }

206_C55 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; }

206_C56 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 using namespace std; //Function Prototype double sinc(double x);

206_C57 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; }

206_C58 Program Using a Function /* This function evaluates the sinc function. */ double sinc(double x) { if (abs(x) < ) return 1.0; else return sin(x)/x; }

206_C59 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

206_C510 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; }

206_C511 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; }

206_C512 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

206_C513 Global/Local Example int count(0);... int main() { int x, y, z;... } int calc(int a, int b) { int x; count += x;... }

206_C514 Summary  Modularity  Programmer Defined Functions  Parameter Passing  Storage Class and Scope

206_C515 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 (%)

206_C516 Example /* This program generates and prints ten random */ /* integers between user-specified limits. */ #include using namespace std; // Function prototype. int rand_int(int a, int b); int main() {...

206_C517 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; }

206_C518 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; }

206_C520 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 reliability Analytical reliability Number of trials Random seed Simulation reliability

206_C521 Problem Solving Applied Hand Example Analytical Reliability  r = 0.8 Series Configuration  r_series = r 3 = Parallel Configuration  r_parallel = 3r - 3r 2 + r 3 = Comp

206_C522 Problem Solving Applied Hand Example Simulation Reliability (3 random trials)    Series Configuration  All must be less than or equal to 0.8  One success = Parallel Configuration  Any must be less than or equal to 0.8  Three successes = 1.0

206_C523 Problem Solving Applied Algorithm Development Read component reliability, number of trials, seed Compute analytical reliabilities While 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 reliabilities Print simulation reliabilities

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

206_C528 Testing

206_C529 Testing

206_C530 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