FCFS - First Come First Serve Code in C, Algorithm, Advantage, Disadvantage

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FCFS - First Come First Serve Code and Algorithm in C.

FCFS - First Come First Serve

First Come First Serve or FCFS is based on First Come First Serve Basis.

Algorithm of FCFS:

• Which process comes first to CPU, the process will serve then.
• It is mainly a non preemptive scheduling algorithm. That means, no stop of a process when that's running.
• FCFS implements the First In First Out (FIFO) algorithm. That means which come first to the queue,  that will out first from the queue.

C Code of FCFS / First Come First Serve C implementation:

#include<stdio.h>

int main()
{
    int n, burst_time[100], waiting_time[100], turn_around_time[100];
    int average_wating_time=0,average_turn_around_time=0;

    printf("Total Processes : ");
    scanf("%d",&n);

    int i, j;
    printf("\nEnter Burst Time : \n");
    for(i=0; i<n; i++)
    {
        printf("P%d = ",i+1);
        scanf("%d",&burst_time[i]);
    }

    waiting_time[0]=0;
    for(i=1; i<n; i++)
    {
        waiting_time[i]=0;
        for(j=0; j<i; j++){
            waiting_time[i] = waiting_time[i] + burst_time[j];
        }

    }


    printf("\n--------------------------------------------------------------");
    printf("\nProcess\t\tBurst Time\tWaiting Time\tTurn around Time");
    printf("\n--------------------------------------------------------------\n");

    for(i=0; i<n; i++)
    {
        turn_around_time[i] = burst_time[i] + waiting_time[i];
        average_wating_time += waiting_time[i];
        average_turn_around_time += turn_around_time[i];
        printf("\nProcess = %d\t\t%d\t\t%d\t\t%d", i+1, burst_time[i], waiting_time[i], turn_around_time[i]);
    }

    average_wating_time = average_wating_time/n;
    average_turn_around_time = average_turn_around_time / n;


    printf("\n\nAverage Waiting Time:%d", average_wating_time);
    printf("\nAverage Turnaround Time:%d\n\n", average_turn_around_time);

    return 0;
}

Output of FCFS:

Explanation of First Come First Serve Algorithm (FCFS)

1) First take the burst time for processes in an array called burst_time[], in these lines,

    for(i=0; i<n; i++)
    {
        printf("P%d = ",i+1);
        scanf("%d",&burst_time[i]);
    }

2) Then check waiting time. For our first process which waiting time = 0 and for what.

    waiting_time[0]=0;

3) Then in the waiting_time[] put the waiting times using waiting_time = waiting_time + burst_time for that process. In these lines,

    for(i=1; i<n; i++)
    {
        waiting_time[i]=0;
        for(j=0; j<i; j++){
            waiting_time[i] = waiting_time[i] + burst_time[j];
        }

    }

4) Then Find the turn around time, average waiting time in these lines,

    for(i=0; i<n; i++)
    {
        turn_around_time[i] = burst_time[i] + waiting_time[i];
        average_wating_time += waiting_time[i];
        average_turn_around_time += turn_around_time[i];
        printf("\nProcess = %d\t\t%d\t\t%d\t\t%d", i+1, burst_time[i], waiting_time[i], turn_around_time[i]);
    }

5) Find Average waiting time and average turn around time by dividing the n, in these lines-

    average_wating_time = average_wating_time/n;
    average_turn_around_time = average_turn_around_time / n;

Advantages of FCFS or First Come First Serve Algorithm:

• FCFS is suitable for batch system, basically.
• FCFS is easier to implement.

Disadvantages of FCFS or First Come First Serve Algorithm:

Note:Having any problems in this First Come First Serve algorithm or code, please comment here and don't hesitate.

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