modified and updated

OS/C/Week10/q2.c

@@ -0,0 +1,169 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <limits.h> // For INT_MAX
+
+// Structure to represent a frame and its last used time
+typedef struct {
+    int page_number;
+    int last_used_time;
+} Frame;
+
+// Function to find if a page exists in frames and return its index
+// Also updates the last_used_time if found
+int find_page(Frame frames[], int n_frames, int page, int current_time) {
+    for (int i = 0; i < n_frames; i++) {
+        if (frames[i].page_number == page) {
+            frames[i].last_used_time = current_time; // Update time on hit
+            return i; // Page found (Hit)
+        }
+    }
+    return -1; // Page not found (Fault)
+}
+
+// Function to find the index of the Least Recently Used (LRU) page
+int find_lru_index(Frame frames[], int n_frames) {
+    int min_time = INT_MAX;
+    int lru_index = 0;
+    for (int i = 0; i < n_frames; i++) {
+        // Frame must contain a valid page (not -1)
+        if (frames[i].page_number != -1 && frames[i].last_used_time < min_time) {
+            min_time = frames[i].last_used_time;
+            lru_index = i;
+        }
+    }
+    return lru_index;
+}
+
+// Function to print the current state of frames
+void print_frames(Frame frames[], int n_frames) {
+    printf("[");
+    for (int i = 0; i < n_frames; i++) {
+        if (frames[i].page_number == -1) {
+            printf(" - ");
+        } else {
+            printf(" %d ", frames[i].page_number);
+        }
+    }
+    printf("]\n");
+}
+
+int main() {
+    int n_frames, n_pages;
+    int *pages = NULL; // Reference string
+    Frame *frames = NULL; // Frames in memory
+
+    int page_faults = 0;
+    int page_hits = 0;
+    int current_time = 0; // Counter to track usage time
+    int frame_idx = 0; // Index for filling empty frames initially
+
+    // 1. Get Inputs
+    printf("Enter the number of frames: ");
+    if (scanf("%d", &n_frames) != 1 || n_frames <= 0) {
+        fprintf(stderr, "Error: Invalid number of frames.\n");
+        return 1;
+    }
+
+    printf("Enter the number of pages in the reference string: ");
+    if (scanf("%d", &n_pages) != 1 || n_pages <= 0) {
+        fprintf(stderr, "Error: Invalid number of pages.\n");
+        return 1;
+    }
+
+    // 2. Allocate Memory
+    pages = (int *)malloc(n_pages * sizeof(int));
+    if (pages == NULL) {
+        perror("Failed to allocate memory for pages");
+        return 1;
+    }
+
+    frames = (Frame *)malloc(n_frames * sizeof(Frame));
+    if (frames == NULL) {
+        perror("Failed to allocate memory for frames");
+        free(pages); // Clean up already allocated memory
+        return 1;
+    }
+
+    printf("Enter the page reference string (space-separated %d integers):\n", n_pages);
+    for (int i = 0; i < n_pages; i++) {
+        if (scanf("%d", &pages[i]) != 1) {
+             fprintf(stderr, "Error reading page reference string.\n");
+             free(pages);
+             free(frames);
+             return 1;
+        }
+    }
+
+    // 3. Initialize Frames
+    for (int i = 0; i < n_frames; i++) {
+        frames[i].page_number = -1; // -1 indicates empty frame
+        frames[i].last_used_time = -1; // Initialize time
+    }
+
+    printf("\n--- LRU Simulation Start ---\n");
+    printf("Frames: %d | Reference String Length: %d\n\n", n_frames, n_pages);
+
+    // 4. Process Page References
+    for (int i = 0; i < n_pages; i++) {
+        current_time++; // Increment time step for each reference
+        int current_page = pages[i];
+        printf("Ref: %d -> ", current_page);
+
+        int found_index = find_page(frames, n_frames, current_page, current_time);
+
+        if (found_index != -1) {
+            // Page Hit
+            page_hits++;
+            printf("Hit   ");
+        } else {
+            // Page Fault
+            page_faults++;
+            printf("Fault ");
+
+            // Find a place for the new page
+            int replace_index = -1;
+
+            // Check for an empty frame first
+            for(int k=0; k < n_frames; k++){
+                if(frames[k].page_number == -1){
+                    replace_index = k;
+                    break;
+                }
+            }
+
+            if (replace_index != -1) {
+                // Use the empty frame
+                frames[replace_index].page_number = current_page;
+                frames[replace_index].last_used_time = current_time;
+                 printf("(loaded into empty frame %d) ", replace_index);
+            } else {
+                // No empty frames, find LRU page to replace
+                replace_index = find_lru_index(frames, n_frames);
+                printf("(replaced P%d in frame %d) ", frames[replace_index].page_number, replace_index);
+                frames[replace_index].page_number = current_page;
+                frames[replace_index].last_used_time = current_time;
+            }
+        }
+        print_frames(frames, n_frames); // Show frame status after each step
+    }
+
+    // 5. Output Results
+    printf("\n--- LRU Simulation End ---\n");
+    printf("Total Page References: %d\n", n_pages);
+    printf("Total Page Hits:    %d\n", page_hits);
+    printf("Total Page Faults:  %d\n", page_faults);
+    if (n_pages > 0) {
+        printf("Hit Rate:           %.2f%%\n", (double)page_hits / n_pages * 100.0);
+        printf("Fault Rate:         %.2f%%\n", (double)page_faults / n_pages * 100.0);
+    } else {
+        printf("Hit Rate:           N/A\n");
+        printf("Fault Rate:         N/A\n");
+    }
+
+
+    // 6. Free Memory
+    free(pages);
+    free(frames);
+
+    return 0;
+}