Principles of Computer Science I Honors Section

Principles of Computer Science IHonors Section Note Set 3 CSE 1341

Today: Arrays – Part 1

The Array • Array • Can store multiple pieces of data • Homogeneous-typed data structure • Stored contiguously in memory • Each piece of data is an element • Each element can be accessed with one identified and an index.

The Array h[0] ? • Arrays are zero subscripted. • Contiguous in memory • amt. of memory = size of datatype * number of elements Basic Declaration: int h[10]; ? h[1] ? h[2] ? h[3] ? h[4] ? h[5] ? h[6] ? h[7] ? h[8] ? h[9]

Array Declaration and Initialization int n[3] = {2, 4, 6}; Initialization List 2 ? ? 4 ? 6 n[0] n[1] n[2] int g[3] = {9}; Partial Initialization List 9 ? ? 0 ? 0 g[0] g[1] g[2]

Size Declarators • Size declarators must be literals or named constants • Cannot be a variable • Compiler needs to know how much memory to set aside for the array. int temp; cin >> temp; int myArray[temp];

Accessing Array Elements • Name of an array is like a constant pointer to a location in memory • Name of array used with a subscript to access individual elements of the array int g[5] = {9, 4, 2}; g[0] = 0; for (int i=0; i<4; i++) g[i]++; subscript – bracket notation subscript can be a variable

“Off By One” and No Bounds Checking int g[35] = {0}; int i = 0; cout << “Let’s enter some grades!”; for (i = 0; i <= 35; i++) { ... } • Past the end of the array • Compiler doesn’t care if you do this • Not a syntax error but almost always a logic error

Some Grades… int g[35] = {0}; int i = 0; cout << “Let’s enter some grades!”; for (i = 0; i < 35; i++) { cout << “Enter a grade or -1 to quit: “; cin >> g[i]; if(g[i] == -1) break; }

Passing Some Grades to a Function int g[35] = {0}; int i = 0; cout << “Let’s enter some grades!”; for (i = 0; i < 35; i++) { cout << “Enter a grade or -1 to quit: “; cin >> g[i]; if(g[i] == -1) break; } average(g, i); Just sending a memory address double average(int g[], int sz) { int sum = 0; for (int i = 0; i < sz; i++) sum += g[i]; return static_cast<float>(sum)/sz; }

Arrays to Functions • When passing arrays to functions • function call has no [ ] • function header & prototype have empty [ ] • the array is always passed by “reference” • you’re just passing a memory address

Character Arrays null-terminated c-string char fName[] = “Mark”; char lName[] = “Fontenot”; cout << lName << “, “ << fName << endl; • You can display the entire c-string by passing the name of the array to cout • DOES NOT WORK FOR numerical-basedarrays

char pWord[25]; cin >> pWord; Will read characters to the first white-space character

Remember… • Arrays are zero-subscripted • last subscript is SizeDeclarator – 1 • Use subscripts to access array • Arrays are always passed by reference • Array contents cannot be copied with = operator – must use loop

Questions??? ?

Principles of Computer Science I Honors Section