LRTF.c

//Write a program to implement Longest-Remaining-Time-First Process Scheduling Algorithm
#include <stdio.h>
struct process
{
	char name;
	int at, bt, ct, wt, tat, rt, rbt;
};
void main()
{
	int n;
	printf("\nEnter the number of processes that you want to insert: \n");
	scanf("%d", &n);
	int i;
	struct process p[n];
	for (i = 0; i < n; i++) //fetching processes's info
	{
		printf("Process: ");
		scanf(" %c", &p[i].name);
		printf("Arrival Time: ");
		scanf(" %d", &p[i].at);
		printf("Burst Time: ");
		scanf(" %d", &p[i].bt);
		p[i].rbt = p[i].bt;
	}
	/*for(i=0;i<n;i++) //checking if all inputs are being stored correctly
	{
		printf("\nProcess: %c",p[i].name);
		printf("\nAT: %d",p[i].at);
		printf("\nBT: %d",p[i].rbt);
	}
	*/
	int t; //clock variable
	t = 0;
	int lp; //points to the longest process
	lp = 0;
	int flag;
	printf("\nGantt chart is as follows:-\n");
	printf(" (0)|");
	while (1)
	{

		for (i = 0; i < n; i++)
		{

			if (t >= p[i].at && p[i].rbt > 0) //checks if process is in ready queue and not completed
			{
				//finds the index of the process with longest remaining time that is to be executed next.

				if (p[i].rbt > p[lp].rbt)
					lp = i;
				else if (p[i].rbt == p[lp].rbt)
					if (p[i].at < p[lp].at)
						lp = i;
			}

		}
		printf(" %c(%d) |", p[lp].name, t + 1); //prints executing process
		if (p[lp].rbt == p[lp].bt) //stores first response time for each process
			p[lp].rt = t;
		p[lp].rbt--; // process execution
		t++;
		if (p[lp].rbt == 0) //stores completion time for each process
			p[lp].ct = t;
		int temp;
		temp = 0;
		do
		{
			lp = (lp + 1) % n;
			if (temp > n) //so that lp makes only one cycle around the ready queue
				break;
			temp++;
		} while (p[lp].rbt <= 0 || t < p[lp].at);
		flag = 0;
		for (i = 0; i < n; i++) //checks if there is any unfinished process
		{
			if (p[i].rbt > 0)
				flag = 1;
		}
		if (flag == 0) //when there are no unfinished processes
			break;
	}
	float sct, srt, swt, stat;
	sct = srt = swt = stat = 0.0;
	printf("\n");

	//prints process info table

	printf("\nProc \t AT \t BT \t CT \t RT \t  WT \t TAT \n");
	for (i = 0; i < n; i++)
	{
		//calculate RT, TAT and WT

		p[i].rt -= p[i].at;
		p[i].tat = p[i].ct - p[i].at;
		p[i].wt = p[i].tat - p[i].bt;
		swt += p[i].wt;
		stat += p[i].tat;
		srt += p[i].rt;
		sct += p[i].ct;

		//prints info for each process

		printf("%c \t %d \t %d \t %d \t %d \t %d \t %d \n", p[i].name, p[i].at, p[i].bt, p[i].ct, p[i].rt, p[i].wt, p[i].tat);
	}

	printf("\nAverage Waiting Time: %f\n", (swt / n));
	printf("Average TurnAround Time: %f\n", (stat / n));
	printf("Average Response Time: %f\n", (srt / n));
	printf("Average Completion Time: %f\n", (sct / n));

}