DESCRIPTION:-

Scheduling of processes/work is done to finish the work on time.
Below are different times with respect to a process.

Arrival Time: Time at which the process arrives in the ready queue.
Completion Time: Time at which process completes its execution.
Burst Time: Time required by a process for CPU execution.
Turn Around Time: Time Difference between completion time and arrival time.

Turn Around Time=Completion Time-Arrival Time

Waiting Time(W.T): Time Difference between turn around time and burst time.

Waiting Time=Turn Around Time-Burst Time.

FCFS Scheduling-

In FCFS Scheduling,
The process which arrives first in the ready queue is firstly assigned the CPU.
In case of a tie,process with smaller process id is executed first.
It is always non-preemptive in nature.

CODE:-

#include<stdio.h>
int main()
{   
    int at[10],at2[10],bt[100],ex[100],seq[100],re[100],wt[100],tat[100];
    int n,i,j,start,pos,max=0,min,idle=0,k=0;
    float av1=0,av2=0;

    printf("*****INPUT*****\n");
    printf("Enter number of process\n");
    scanf("%d",&n);
    printf("Enter arrival time for processess\n");
    for(i=0;i<n;i++)
    {
     scanf("%d",&at[i]);
     at2[i]=at[i];
    }
    printf("Enter burst time for processess\n");
    for(i=0;i<n;i++)
    {
     scanf("%d",&bt[i]);
    }
    start=at[0];
    for(i=1;i<n;i++)
    {
      if(start>at[i])
       {
       start=at[i];
       }
     }
    printf("*****OUTPUT*****\n");
    printf("Sequence of execution is\n");
    for(i=0;i<n;i++)
    {
    if(max<at[i])
     {
      max=at[i];
     }
    }
    max=max+1;
   for(i=0;i<n;i++,k++)
     {  min=max;
       for(j=0;j<n;j++){  
           if(at[j]!=-1)
             {
               if(at[j]<min)
                 {
                  min=at[j];
                  pos=j;
                 }
              }
         }
      printf("[P%d]  ",pos);
      seq[k]=pos;
      if(start<at[pos]){
         re[pos]=start;
         idle+=at[pos]-start;
         start=at[pos];
         start+=bt[pos];
         at[pos]=-1;
         ex[pos]=start;
      }
      else{
        re[pos]=start;
        start+=bt[pos];
        at[pos]=-1;
        ex[pos]=start;
       }
     }
    printf("\n");
    for(i=0;i<n;i++)
    {
       tat[i]=ex[i]-at2[i];
       wt[i]=tat[i]-bt[i];
    }
 printf("Process  Arrival-time(s)  Burst-time(s)  Waiting-time(s)  Turnaround-time(s)\n");
   for(i=0;i<n;i++)
    {
      printf("P%d            %d              %d             %d               %d\n",i,at2[i],bt[i],wt[i],tat[i]);
    }
   for(i=0;i<n;i++)
   {
    av1+=tat[i];
    av2+=wt[i];
   }
  printf("Average waiting time(s) %f\nAverage turnaroundtime(s) %f\nCPU idle time(s)%d\n",av2/n,av1/n,idle);
}

OUTPUT:-

*****INPUT*****
Enter number of process
5
Enter arrival time for processess
3 5 0 5 4
Enter burst time for processess
4 3 2 1 3
*****OUTPUT*****
Sequence of execution is
[P2]  [P0]  [P4]  [P1]  [P3]
Process  Arrival-time(s)  Burst-time(s)  Waiting-time(s)  Turnaround-time(s)

P0           3            4                0             4
P1           5            3                5             8
P2           0            2                0             2
P3           5            1                8             9
P4           4            3                3             6

Average waiting time(s) 3.200000
Average turn around time(s) 5.800000
CPU idle time(s)1
Process returned 0 (0x0)   execution time : 35.057 s
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