Introduction to C Programming CE Lecture 11 Sorting and Searching using Arrays

Searching and sorting Lists of data often stored in arrays May be complex data Use arrays of structs Many standard processes require searching and sorting

Linear Search Suitable for sorted or unsorted list Starts at beginning of array and checks each element against a target Loops for number of items in the list Returns position in array of found item or value representing not found Position used to retrieve data

Linear Search Target value =  Position found = Index = 0 Index = 1 Index = 2 Index = 3

Linear Search Target value =  Position found = Index = 0 Index = 1 Index = 2 Index = Index = Index = 5

Searching an array of structs Same process Use one of the fields to search e.g. birthdays[listindex].month Returns position in array as before

Bubble Sort Sort needed for variety of reasons Can be ascending or descending Sorted data often required for more efficient searching algorithms Bubble sort one of the simplest Each complete pass results in the highest unsorted item ‘bubbling’ to the end.

First Pass Compare 0, Compare 1,2 Compare 2,3 Compare 3,4 Compare 4,5

Second Pass Compare 0,1 Compare 1,2 Compare 2,3 Compare 3,4

Third Pass Compare 0,1 Compare 1,2 Compare 2,3

Sorting array of structs Same principle as for single data arrays One of the fields is used to perform the comparison E.g. birthdays [i].month > birthdays[i+1].month If a swap is needed the whole structs are swapped

Abstract Data Types System stack and System Heap deployed by system calls (stack used in assembler) Stack concept can be implemented by programmer Known as Abstract Data Type or ADT Main types are Stacks and Queues Can be implemented using various data structures

Stack and Queue

Addition to a stack (push) push (item, stack) begin if top = n then stackfull else begin increment top stack(top) = item end end Deletion from a stack (pop) pop(item, stack) begin if top = 0 then stackempty else begin item = stack[top] top = top-1 end end

Array Implementation of Stack /* Implements a stack using an array */ #include int main(void) { int data, i, max; int top = 0; int stack[100]; printf("\nStack size? "); scanf("%d", &max); for (i = 0; i <= max; i++) { stack[i] = 0; } while (top <= max-1) { printf("\nEnter an integer: "); scanf("\n%d", &data); top++; stack[top] = data; } printf("\nPopping data off the stack:\n\n"); while (top >= 1) { printf("%d\n", stack[top]); top--; } printf("\n"); return 0; }

Deletion from a queue (dequeue) deleteq (item, queue) begin if front = rear then queueempty else begin item = q[front] front = front+1 end end Addition into a queue addq (item, queue) begin if rear=n then queuefull else begin rear :=rear+1; q[rear]:=item; end end

Array Implementation of Queue /* queue.c */ /* Implements a queue using an array */ /* queues and enqueues via functions */ #include /* Prototypes */ int enqueue(int, int [],int ); int dequeue(int, int [],int );

Array Implementation of Queue int main(void) { int i, max, response; int rear = 0, front = 0; /* set front & rear */ int queue[100]; printf("\nqueue size? "); scanf("%d", &max); for (i = 0; i <= max; i++) { queue[i] = 0; } printf(" enter a choice (zero to exit): "); scanf("%d", &response);

Array Implementation of Queue while (response != 0) { if (response == 1) { rear = enqueue(rear,queue,max); } else { front = dequeue(front, queue, rear); } printf(" enter a choice : "); scanf("%d",&response); } printf("\n"); return 0; }

Array Implementation of Queue int enqueue(int rear, int queue[],int max) { if (rear <= max) /* if rear not at end of queue */ { int value; printf("\nEnter an integer to add: "); scanf("\n%d", &value); queue[rear] = value; displayqueue(rear,queue); rear++;/* bump to next available slot */ } return rear; }

Array Implementation of Queue int dequeue(int front, int queue[],int rear) { if (front < rear) { printf("\nremoving data from front of queue:"); /* go back to first value added */ printf("%d\n", queue[front]); queue[front] = 0; displayqueue(rear-1,queue); front++; } return front; }