Computer Science 210 Computer Organization Arrays

The Array Structure A linear sequence of memory cells, each accessible by an an integer index, ranging from 0 to the number of cells minus 1 Like Python lists and Java array lists, C arrays support random (constant-time) access to the cells

int integers[10]; // Cells for 10 ints char letters[5]; // Cells for 5 characters float matrix[3][2]; // A 3 by 2 matrix of floats int max = 100; // The number of cells in the next array double doubles[max]; // Cells for max doubles Declaring Array Variables The syntax [ ] declares an array variable and reserves memory for a definite number of cells (use more [] for more dimensions), each of which can store an element of the given type (arrays are statically typed) Each cell initially contains garbage!

Initializing and Processing int i, max = 10, array[max]; // Declare variables for (i = 0; i < max; i++) // Store 1..max in the array array[i] = i + 1; for (i = 0; i < max; i++) // Print the contents printf("%d\n", array[i]); Here we initialize all of the array’s cells and visit them all The loop is pretty standard

Initializing Arrays that Are Not Full int number, length = 0, max = 10, array[max]; printf("Enter a number or 0 to stop: "); scanf("%d", &number); while (number){ array[length] = number; length++; if (length == max){ printf("Maximum number of numbers entered\n"); break; } printf("Enter a number or 0 to stop: "); scanf("%d", &number); } The number of data values is tracked with a separate variable This length variable is also used in processing the array later

Processing Arrays that Are Not Full int number, length = 0, max = 10, array[max]; // Get the array’s data and length here // Print all of the currently available values int i; for (i = 0; i < length; i++) printf("%d\n", array[i]); The number of data values is tracked with a separate variable This length variable is also used in processing the array later

Arrays and Functions #include #include "numbers.h" // Use a library of array processing functions int main(){ int max = 100; int numbers[max]; int length = getNumbers(numbers, max); if (length > 0) printf("The average is %f\n", sum(numbers, length) / (double) length); else printf("No numbers were entered\n"); } An array can be passed as an argument to a function The function can access or replace values in the array cells

Example: Find the Minimum // Returns the index of the minimum value in the array int minIndex(int array[], int length){ int probe, minPos = 0; for (probe = 1; probe < length; probe++) if (array[probe] < array[minPos]) minPos = probe; return minPos; } The element type of the array parameter must be specified, but its physical size need not be Therefore, this function can process an integer array of any physical size The logical size ( length ) is passed too, because the array might not be full

How Parameters Are Passed to Functions Parameters of basic types ( char, int, float, and double ) are passed by value (a copy of the value of the argument is placed in temporary storage on the runtime stack) A copy of an array’s base address is also placed in temporary storage, so its cells can still be accessed or modified