Practicals
Semester-05
OSL
Assignment 03

Assignment-03

Title

Implement the C program for CPU Scheduling Algorithms: Shortest Job First (Preemptive) and Round Robin with different arrival time.

Theory

Shortest Job First (SJF) is a non-preemptive or preemptive scheduling algorithm that selects the waiting process with the smallest execution time to execute next. In the preemptive version, if a new process arrives with a shorter burst time than the currently running process, the currently running process is preempted and placed back into the ready queue.

Code Implementation

#include<stdio.h>
 
struct Process {
    int pid;
    int arrival_time;
    int burst_time;
    int remaining_time;
    int completion_time;
    int turnaround_time;
    int waiting_time;
};
 
void swap(struct Process *xp, struct Process *yp) {
    struct Process temp = *xp;
    *xp = *yp;
    *yp = temp;
}
 
void bubbleSort(struct Process arr[], int n) {
    int i, j;
    for (i = 0; i < n-1; i++) {
        for (j = 0; j < n-i-1; j++) {
            if (arr[j].arrival_time > arr[j+1].arrival_time) {
                swap(&arr[j], &arr[j+1]);
            }
        }
    }
}
 
int main() {
    int n, i, time = 0, total_burst_time = 0;
    printf("Enter the number of processes: ");
    scanf("%d", &n);
 
    struct Process processes[n];
 
    // Input process details
    for(i = 0; i < n; i++) {
        processes[i].pid = i + 1;
        printf("Enter the arrival time for process %d: ", processes[i].pid);
        scanf("%d", &processes[i].arrival_time);
        printf("Enter the burst time for process %d: ", processes[i].pid);
        scanf("%d", &processes[i].burst_time);
        processes[i].remaining_time = processes[i].burst_time;
        total_burst_time += processes[i].burst_time;
    }
 
    bubbleSort(processes, n);
 
    printf("\nGantt Chart: ");
    printf("\n| Time | Process |");
 
    while(total_burst_time > 0) {
        int shortest_index = -1, shortest_burst_time = 99999;
        for(i = 0; i < n; i++) {
            if(processes[i].arrival_time <= time && processes[i].remaining_time > 0) {
                if(processes[i].remaining_time < shortest_burst_time) {
                    shortest_burst_time = processes[i].remaining_time;
                    shortest_index = i;
                }
            }
        }
 
        if(shortest_index == -1) {
            printf("\n| %3d  |  Idle   |", time);
            time++;
            continue;
        }
 
        processes[shortest_index].remaining_time--;
        total_burst_time--;
        time++;
 
        printf("\n| %3d  |    P%d   |", time, processes[shortest_index].pid);
    }
 
    printf("\n\nProcess\t Turnaround Time\t Waiting Time\n");
    for(i = 0; i < n; i++) {
        processes[i].turnaround_time = processes[i].completion_time - processes[i].arrival_time;
        processes[i].waiting_time = processes[i].turnaround_time - processes[i].burst_time;
        printf("P%d\t\t%d\t\t\t%d\n", processes[i].pid, processes[i].turnaround_time, processes[i].waiting_time);
    }
 
    return 0;
}

Setup and Run

  1. Compile the program using any C compiler (e.g., gcc).
  2. Run the compiled executable file.
  3. Enter the number of processes, arrival time, and burst time for each process when prompted.
  4. View the Gantt chart and the process turnaround time and waiting time.

Example

Enter the number of processes: 3
Enter the arrival time for process 1: 0
Enter the burst time for process 1: 6
Enter the arrival time for process 2: 1
Enter the burst time for process 2: 4
Enter the arrival time for process 3: 2
Enter the burst time for process 3: 8

Output:

Gantt Chart:
| Time | Process |
|   1  |    P1   |
|   2  |    P2   |
|   3  |    P2   |
|   4  |    P2   |
|   5  |  Idle   |
|   6  |    P1   |
|   7  |    P3   |
|   8  |    P3   |
|   9  |    P3   |
|  10  |    P3   |
|  11  |    P3   |
|  12  |    P3   |
|  13  |    P3   |
|  14  |    P3   |

Process	 Turnaround Time	 Waiting Time
P1		6			0
P2		3			0
P3		11			3

Contact

For any questions or clarifications, please contact Parth Sali at parthsali04@gmail.com.

Assignment 02 BAssignment 04 A