Write the simulation program for demand paging and show the page scheduling and total number of page faults according the MRU page replacement algorithm. Assume the memory of n frames.
Reference String :    3, 4, 5, 6, 3, 4, 7, 3, 4, 5, 6, 7, 2, 4, 6


#include <stdio.h>
#include <stdlib.h>

#define MAX_FRAMES 100
#define REFERENCE_STRING_LENGTH 15

// Function prototypes
void print_memory(int memory[], int num_frames);
int find_most_recently_used(int memory[], int num_frames, int usage[], int usage_index);

int main() {
    int memory[MAX_FRAMES];
    int reference_string[REFERENCE_STRING_LENGTH] = {3, 4, 5, 6, 3, 4, 7, 3, 4, 5, 6, 7, 2, 4, 6};
    int num_frames; // Number of frames in memory
    int num_references = REFERENCE_STRING_LENGTH; // Length of the reference string
    int page_faults = 0;
    int usage[MAX_FRAMES]; // To track the most recently used pages
    int usage_index = 0; // Index to keep track of MRU

    // Initialize the memory with -1 (indicating empty frames)
    printf("Enter the number of frames: ");
    scanf("%d", &num_frames);

    if (num_frames > MAX_FRAMES) {
        printf("Number of frames exceeds maximum limit.\n");
        return 1;
    }

    // Initialize memory and usage arrays
    for (int i = 0; i < num_frames; i++) {
        memory[i] = -1;
    }

    // Process each page in the reference string
    for (int i = 0; i < num_references; i++) {
        int current_page = reference_string[i];
        int page_found = 0;

        // Check if the page is already in memory
        for (int j = 0; j < num_frames; j++) {
            if (memory[j] == current_page) {
                page_found = 1;
                // Update usage order
                usage[usage_index] = current_page;
                usage_index = (usage_index + 1) % num_frames; // Circular increment
                break;
            }
        }

        if (!page_found) {
            // Page fault
            page_faults++;
            printf("Page fault! Reference: %d\n", current_page);

            if (usage_index < num_frames) {
                // Add new page to memory
                memory[usage_index] = current_page;
                usage[usage_index] = current_page;
                usage_index = (usage_index + 1) % num_frames; // Circular increment
            } else {
                // Replace the most recently used page
                int mru_page = find_most_recently_used(memory, num_frames, usage, usage_index);
                for (int j = 0; j < num_frames; j++) {
                    if (memory[j] == mru_page) {
                        memory[j] = current_page;
                        break;
                    }
                }
                // Update usage order
                usage[usage_index] = current_page;
                usage_index = (usage_index + 1) % num_frames; // Circular increment
            }
        } else {
            printf("Page hit! Reference: %d\n", current_page);
        }

        // Print the state of memory
        print_memory(memory, num_frames);
    }

    printf("Total number of page faults: %d\n", page_faults);

    return 0;
}

// Function to print the state of the memory
void print_memory(int memory[], int num_frames) {
    printf("Memory state: ");
    for (int i = 0; i < num_frames; i++) {
        if (memory[i] != -1) {
            printf("%d ", memory[i]);
        } else {
            printf("_ ");
        }
    }
    printf("\n");
}

// Function to find the most recently used page
int find_most_recently_used(int memory[], int num_frames, int usage[], int usage_index) {
    int mru_page = usage[(usage_index - 1 + num_frames) % num_frames];
    for (int i = 0; i < num_frames; i++) {
        if (memory[i] == mru_page) {
            return mru_page;
        }
    }
    return -1; // Should never reach here if logic is correct
}