FCFS and SJF CPU Scheduling C Program Example

FCFS and SJF CPU Scheduling C Program Example

Corrected and formatted C source code for FCFS and SJF scheduling.

FCFS Scheduling C Implementation

#include <stdio.h>

int FCFS() {
    int bt[15], n, i, wt[15];
    float twt = 0, tat = 0, att, awt;
    printf("\nTHE FCFS SCHEDULING\n");
    printf("Enter the number of processes: ");
    scanf("%d", &n);
    printf("Enter burst time of all the processes:\n");
    for (i = 0; i < n; i++) {
        printf("P%d: ", i + 1);
        scanf("%d", &bt[i]);
    }

    wt[0] = 0;
    // for calculating waiting time of each process
    for (i = 1; i < n; i++)
        wt[i] = bt[i - 1] + wt[i - 1];

    printf("ProcessID\tBurstTime\tWaitingTime\tTurn Around Time\n");
    for (i = 0; i < n; i++) {
        printf("P%d\t\t%d\t\t%d\t\t%d\n", i + 1, bt[i], wt[i], bt[i] + wt[i]);
        // calculating total waiting time
        twt += wt[i];
        // for calculating total turn around time
        tat += (wt[i] + bt[i]);
    }

    // for calculating average waiting time
    awt = twt / n;
    // for calculating average turn around time
    att = tat / n;
    printf("\nAvg. waiting time = %f\n", awt);
    printf("Avg. turn around time = %f\n", att);
    return 0;
}

SJF Scheduling C Implementation

int SJF() {
    int bt[20], p[20], wt[20], tat[20], i, j, n, total = 0, pos, temp;
    float avg_wt, avg_tat;
    printf("\nTHE SJF SCHEDULING\n");
    printf("Enter the number of process: ");
    scanf("%d", &n);
    printf("\nEnter Burst time:\n");
    for (i = 0; i < n; i++) {
        printf("P%d: ", i + 1);
        scanf("%d", &bt[i]);
        p[i] = i + 1;
    }

    // sorting of burst times (selection sort)
    for (i = 0; i < n; i++) {
        pos = i;
        for (j = i + 1; j < n; j++) {
            if (bt[j] < bt[pos])
                pos = j;
        }
        temp = bt[i];
        bt[i] = bt[pos];
        bt[pos] = temp;
        temp = p[i];
        p[i] = p[pos];
        p[pos] = temp;
    }

    wt[0] = 0;
    for (i = 1; i < n; i++) {
        wt[i] = 0;
        for (j = 0; j < i; j++)
            wt[i] += bt[j];
        total += wt[i];
    }

    avg_wt = (float) total / n;
    total = 0;
    printf("\nProcess\tBurstTime\tWaiting Time\tTurn around time\n");
    for (i = 0; i < n; i++) {
        tat[i] = bt[i] + wt[i];
        total += tat[i];
        printf("P%d\t%d\t\t%d\t\t%d\n", p[i], bt[i], wt[i], tat[i]);
    }
    avg_tat = (float) total / n;
    printf("\n\nAverage Waiting Time = %f", avg_wt);
    printf("\nAverage Turnaround Time = %f\n", avg_tat);
    return 0;
}

Main Function

int main() {
    FCFS();
    SJF();
    return 0;
}

Notes

• This code implements FCFS and SJF CPU scheduling in C.
• Arrays are sized to support up to 15 or 20 processes where declared.
• Input: number of processes and burst times for each process.
• Outputs include waiting time, turn around time, and averages.