Implementation of Priority Queue using Linked List

#include<stdio.h> #include<stdlib.h> int MAX=0;//Max elements in the queue typedef struct mynode { char info; int pri; struct mynode *Link; }Node; Node *start=NULL,*start2=NULL,*Last=NULL; //Full int isFull() { int flag=0; Node *tptr=start; while(tptr) { flag++; tptr=tptr->Link; } if(flag==MAX) return 1; else return 0; } //Empty int isEmpty() { int flag=0; Node *tptr=start; while(tptr) { flag++; tptr=tptr->Link; } /*if(start==NULL) return 1; else return 0;*/ if(flag==0) return 1; else return 0; } //Display Function void display() { Node *tptr=start; printf("\nQUEUE:\n"); while(tptr) { printf("%c->%d\n",tptr->info,tptr->pri); tptr=tptr->Link; } } //High Low Display Function void display_high_low() { int max=0; int min=100; char max_info,min_info; Node *tptr=start,*tptr1=start; while(tptr) { if(tptr->pri>max) { max_info=tptr->info; max=tptr->pri; } tptr=tptr->Link; } while(tptr1) { if(tptr1->pri<min) { min_info=tptr1->info; min=tptr1->pri; } tptr1=tptr1->Link; } printf("Highest Priority:%c->%d\n",max_info,max); printf("Lowest Priority:%c->%d\n",min_info,min); } //Add void add(char v1,int v2) { Node *newp=NULL,*tptr=NULL; newp=(Node*)malloc(sizeof(Node)); newp->info=v1; newp->pri=v2; newp->Link=NULL; if(start==NULL) { start=newp; } else { tptr=start; while(tptr->Link!=NULL) { tptr=tptr->Link; } tptr->Link=newp; Last=newp; } printf("Value Added\n");

} //Delete void del() { int max=0; Node *tptr=start,*tptr1=start,*temp=NULL; while(tptr) { if(tptr->pri>max) { max=tptr->pri; } tptr=tptr->Link; } while(tptr1->pri!=max) { temp=tptr1; tptr1=tptr1->Link; } temp->Link=tptr1->Link; if(tptr1==Last) { Last=temp; } free(tptr1); printf("Value wid max priority deleted\n"); } //Main int main() { char v1; int v2; char choice; printf("Enter the max length of the queue:"); scanf("%d",&MAX); fflush(stdin); printf("MENU:\nA)ADD\nB)REMOVE\nC)DISPLAY\nD)HIGH AND LOW ELEMENT\nE)EXIT\n"); scanf("%c",&choice); fflush(stdin); while(choice!='E') { switch(choice) { case 'A': if(isFull()) { printf("\nQueue Overflow"); } else { printf("Enter the value:"); scanf("%c",&v1); printf("Enter the priority:"); scanf("%d",&v2); add(v1,v2); } break; case 'B': if(isEmpty()) { printf("\nQueue Empty"); } else { del(); } break; case 'C': display(); break; case 'D': display_high_low(); break; default: printf("Invalid Input"); } fflush(stdin); printf("\nMENU:\nA)ADD\nB)REMOVE\nC)DISPLAY\nD)HIGH AND LOW ELEMENT\nE)EXIT\n"); scanf("%c",&choice); fflush(stdin); } printf("Thank You for using our service\n"); return 0; }

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Contributed by: Abhishek Banerjee, CSE, JISCE