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ICOM 4015 Advanced Programming. Lecture 3 Busqueda y Ordenamiento I Reading: LNN Chapters 9,10 & 16. Prof. Bienvenido Vélez. B ú squeda y Ordenamiento. Topic 1 why arrays? declaration/initialization/acess array parameters Topic 2 Searching algorithms Topic 3 Sorting algorithms.
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ICOM 4015 Advanced Programming Lecture 3 Busqueda y Ordenamiento I Reading: LNN Chapters 9,10 & 16 Prof. Bienvenido Vélez ICOM 4015
Búsqueda y Ordenamiento • Topic 1 • why arrays? • declaration/initialization/acess • array parameters • Topic 2 • Searching algorithms • Topic 3 • Sorting algorithms ICOM 4015
Static Arrays I Outline • Why arrays? • Array declaration, initialization and access • Array parameters • Examples of array usage: • statistics on arrays • array reversal ICOM 4015
Why arrays? Want to represent groups of homogeneous objects BUT Do not want nor care to give each group member a different name. Solution: Access members by position ICOM 4015
Statistics - main function // Standard C++ header files #include <cmath> #include <iostream> // Forward declarations of local functions template <class T> T sqr (T x); int readData(); void printReport(int N, float max, float min, float avg, float stdev); // Global definitions const int ArrayLength = 100; float numbers[ArrayLength]; // Main function int main() { // Read data into numbers array int counter = readData(); cout << "Read " << counter << " numbers" << endl; if (counter == 0) return 0; // Compute Max, Min and Avg in first pass float maxDatum = numbers[0]; float minDatum = numbers[0]; float sum = 0; for(int i=0; i<counter; i++) { sum += numbers[i]; maxDatum = (maxDatum > numbers[i]) ? maxDatum : numbers[i]; minDatum = (minDatum < numbers[i]) ? minDatum : numbers[i]; } float avg = sum / counter; // Compute Std deviation in second pass float sumDevs = 0; for(int i=0; i<counter; i++) { sumDevs += sqr(numbers[i] - avg); } float stdev = sqrt(sumDevs / counter); // Print report printReport(counter, maxDatum, minDatum, avg, stdev); } ICOM 4015 stats.cc
StatisticsAuxiliary functions // Auxiliary local functions int readData() { int counter = 0; while(true) { cout << "Next datum: "; float nextDatum; cin >> nextDatum; if (cin.eof()) break; numbers[counter++] = nextDatum; } return counter; } void printReport(int N, float max, float min, float avg, float stdev) { cout << "Report:" << endl; cout << "N: " << N << endl; cout << "Max: " << max << endl; cout << "Min: " << min << endl; cout << "Avg: " << avg << endl; cout << "Std Dev: " << stdev << endl; } template <class T> T sqr (T x) { return x * x;}; stats.cc ICOM 4015
Statistics Output [bvelez@amadeus] ~/icom4015/lec10 >>arrays Next datum: 3 Next datum: 4 Next datum: 5 Next datum: 6 Next datum: Read 4 numbers Report: N: 4 Max: 6 Min: 3 Avg: 4.5 Std Dev: 1.11803 [bvelez@amadeus] ~/icom4015/lec10 >> ICOM 4015
ID[0] ID[1] ID[2] ID[3] ID[4] ID[dim-1] Anatomy of an Array Definition array name type ID [ dim ] element type number of cells starting from 0 Arrays are zero-offset in C++ ICOM 4015
Array BasicsSummary of Concepts • Arrays are compound objects used to represent groups of homogeneous objects • Each cell of an array must have the same type • Array elements are accessed by position (index) • An array of n cells has elements indexed from 0 to n-1 • An attempt to access a cell beyond the boundaries of the array (below 0 or above n-1) may yield runtime errors that are difficult to detect and fix. Check your boundaries! ICOM 4015
Anatomy of an Array Parameter Definition array name int f(int a[], int length) array dimension unspecified type of elements number of cells additional parameter ICOM 4015
Reversing and arrayMain function // Standard C++ header files #include <cmath> #include <iostream> // Forward declarations of local functions template <class T> swap(T& a, T& b); template <class T> int readData(istream& source, T data[], int maxlen); template <class T> void printArray(ostream& sink, T a[], int length); template <class T> void reverseArray(T a[], int length); // Main function int main() { // Define local array to hold input data const int ArrayLength = 100; float numbers[ArrayLength] = { 0.0 }; // Inititalize all cells to 0 // Read data from standard input int counter = readData(cin, numbers, ArrayLength); cout << "Read " << counter << " numbers" << endl; if (counter == 0) return 0; cout << "Original Array:" << endl; printArray(cout, numbers, counter); reverseArray(numbers, counter); cout << "Reversed Array:" << endl; printArray(cout, numbers, counter); } array-params..cc ICOM 4015
Reversing and ArrayAuxiliary Functions // Auxiliary local functions template <class T> int readData(istream& source, T data[], int maxlen) { int counter = 0; while(counter < maxlen) { cout << "Next datum: "; float nextDatum; source >> nextDatum; if (source.eof()) break; data[counter++] = nextDatum; } return counter; } template <class T> void printArray(ostream& sink, T a[], int length) { for (int i=0; i<length; i++) { sink << a[i] << endl; } } template <class T> void reverseArray(T a[], int length) { int iterations = length / 2; for (int i=0; i<iterations; i++) { swap(a[i], a[length - i - 1]); } } template <class T> swap(T& a, T& b) { T temp = a; a = b; b = temp; } ICOM 4015 array-params.cc
Example 1 Output [bvelez@amadeus] ~/icom4015/lec11 >>array-params Next datum: 1 Next datum: 2 Next datum: 3 Next datum: 4 Next datum: 5 Next datum: 6 Next datum: 7 Next datum: 8 Next datum: 9 Next datum: 10 Next datum: Read 10 numbers Original Array: 1 2 3 4 5 6 7 8 9 10 Reversed Array: 10 9 8 7 6 5 4 3 2 1 [bvelez@amadeus] ~/icom4015/lec11 >> ICOM 4015
Array Parameters Summary • Arrays are passed by reference by default • Compiler ignores array dimension in parameter declaration • Programmer typically passes array length as extra parameter. No way to tell array length from array itself. ICOM 4015
