//C Program to Simulate Round Robin CPU Scheduling by Nived Kannada
//NOTE: IN THIS, WE ARE ASSUMING THAT ARRIVAL TIME IS 0 FOR ALL PROCESSES.
#include<stdio.h>
//We are defining functions to calculate Turnaroundtime and waiting time.
//Function to find Turnaround time
int turnarroundtime(int p[], int n,
int bt[], int wt[], int tat[]) {
int i;
for (i = 0; i < n ; i++)
tat[i] = bt[i] + wt[i];
return 1;
}
//Function to calculate waiting time
int waitingtime(int p[], int n,
int bt[], int wt[], int quantum)
{
int rem_bt[n]; //rem_bt is remaining burst time for each process(stored as array). It is initially set as equal to bt[].
//Copying bt[] to rem_bt[]
for (int i = 0 ; i < n ; i++)
rem_bt[i] = bt[i];
int t = 0; //Setting initial time as 0
//Traversing processes in Round Robin manner until all of them are not done.
while (1) {
int finished = 1;
for (int i = 0 ; i < n; i++) //Traversing through each process one by one repeatedly.
{
//We have to process only if remaining burst time of a process is greater than zero.
if (rem_bt[i] > 0) //Checking if remaining burst time of current process is greater than zero.
{
finished = 0; // rem_bt[i]>0 means the current process is not finished yet.
if (rem_bt[i] > quantum) {
t = t+quantum; //Adding time_quantum to current time t.
rem_bt[i] = rem_bt[i] - quantum; //Subtracting time_quantum from remaining burst time.
}
else // ie. if remaining burst time is less than time_quantum
{
t = t + rem_bt[i]; //adding the remaining burst time with current time t.
wt[i] = t - bt[i]; // Waiting time = current time - burst time of current process.
//in this case, rem_bt[i] is less than the time_quantum.
//ie. process will be finished in this cycle. So we can set rem_bt[i] as 0.
rem_bt[i] = 0;
}
}
}
//If all processes are finished
if (finished == 1)
{ break; }
}
return 1;
}
//Main Function
void main()
{
int n, bt[20], at[20],p[20],wt[20],tat[20] ,i, total=0, time_quantum; //Here a new variable is introduced --> time_quantum
int x;
float avgwt=0, avgtat=0;
//Reading number of processes from input.
printf("Enter number of processes: ");
scanf("%d",&n);
//Reading Burst times of all processes. (( ASSUMING ARRIVAL TIME IS 0 FOR ALL PROCESSES. ))
printf("Enter the Burst time value of each process: \n");
for(i=0;i<n;i++)
{
p[i]=i;
at[i]=0;
printf("Burst Time of P[%d]: ",i);
scanf("%d",&bt[i]);
}
//Reading the Time Quantum value
printf("Enter the Time Quantum: ");
scanf("%d",&time_quantum);
//Calling the functions to calculate waiting time and turnaround time
waitingtime(p, n, bt, wt, time_quantum);
turnarroundtime(p, n, bt, wt, tat);
//Displaying Table
printf("\n\tPID\tAT\tBT\tWT\tTAT\n");
for(i=0;i<n;i++)
{
printf("\t%d\t%d\t%d\t%d\t%d\n",p[i],at[i],bt[i],wt[i],tat[i]);
}
//Calculating Average Waiting time and Average Turnaround Time
for(i=0;i<n;i++)
{
avgwt = avgwt + wt[i];
avgtat = avgtat + tat[i];
}
avgwt = avgwt/n;
avgtat = avgtat/n;
//Displaying Average WT and Average TAT
printf("\nAverage WT = %f\n", avgwt);
printf("\nAverage TAT = %f\n", avgtat);
}
//END OF PROGRAM
