C program of round robin scheduling algorithm

 What is round robin scheduling :-

• In this technique ready queue is treated as circular queue.
• In this technique each process is provided a fix time execute which is called time quantum (or time slice). 
• CPU goes around the ready queue allocating the CPU to each process for a time interval up to 1 time quantum.   
• It is only preemptive.
• This algorithm gives minimum average response time for a given set of process.
• Widely used scheduling method in traditional OS.
• It is designed especially for time sharing system or multi-tasking system.

Code:-

#include<stdio.h>

struct process

{

int id,AT,BT,WT,TAT;

};

struct process a[10];

// declaration of the ready queue

int queue[100];

int front=-1;

int rear=-1;

// function for insert the element

// into queue

void insert(int n)

{

if(front==-1)

front=0;

rear=rear+1;

queue[rear]=n;

}

// function for delete the

// element from queue

int delete()

{

int n;

n=queue[front];

front=front+1;

return n;

}

int main()

{

int n,TQ,p,TIME=0;

int temp[10],exist[10]={0};

float total_wt=0,total_tat=0,Avg_WT,Avg_TAT;

printf("Enter the number of the process\n");

scanf("%d",&n);

printf("Enter the arrival time and burst time of the process\n");

printf("AT BT\n");

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

{

scanf("%d%d",&a[i].AT,&a[i].BT);

a[i].id=i;

temp[i]=a[i].BT;

}

printf("Enter the time quantum\n");

scanf("%d",&TQ);

// logic for round robin scheduling

// insert first process

// into ready queue

insert(0);

exist[0]=1;

// until ready queue is empty

while(front<=rear)

{

p=delete();

if(a[p].BT>=TQ)

{

a[p].BT=a[p].BT-TQ;

TIME=TIME+TQ;

}

else

{

TIME=TIME+a[p].BT;

a[p].BT=0;

}

//if process is not exist

// in the ready queue even a single

// time then insert it if it arrive

// at time 'TIME'

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

{

if(exist[i]==0 && a[i].AT<=TIME)

{

insert(i);

exist[i]=1;

}

}

// if process is completed

if(a[p].BT==0)

{

a[p].TAT=TIME-a[p].AT;

a[p].WT=a[p].TAT-temp[p];

total_tat=total_tat+a[p].TAT;

total_wt=total_wt+a[p].WT;

}

else

{

insert(p);

}

}

Avg_TAT=total_tat/n;

Avg_WT=total_wt/n;

// printing of the answer

printf("ID WT TAT\n");

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

{

printf("%d %d %d\n",a[i].id,a[i].WT,a[i].TAT);

}

printf("Average waiting time of the processes is : %f\n",Avg_WT);

printf("Average turn around time of the processes is : %f\n",Avg_TAT);

return 0;

}

Output:-

Enter the number of the process

3

Enter the arrival time and burst time of the process

AT BT

0 5

2 7

4 6

Enter the time quantum

3

ID WT TAT

0 3 8

1 9 16

2 7 13

Average waiting time of the processes is : 6.333333

Average turn around time of the processes is : 12.333333

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