//Write a program in C to implement LRU page replacement algorithm.

#include <stdio.h>

#define MAX_SIZE 50

int main() {
    int n, frameSize;

    // Input the number of pages
printf("Enter the number of pages: ");
scanf("%d", &n);

    int pages[MAX_SIZE];

    // Input the page reference string
printf("Enter the page reference string:\n");
    for (int i = 0; i< n; i++) {
printf("Enter page %d: ", i + 1);
scanf("%d", &pages[i]);
    }

    // Input the size of the page frame
printf("Enter the size of the page frame: ");
scanf("%d", &frameSize);

    int frame[frameSize];
    int pageFaults = 0;

    // Initialize the frame to -1 (indicating empty frame)
    for (int i = 0; i<frameSize; i++) {
        frame[i] = -1;
    }

    // Create an array to store the last used time of each page
    int lastUsedTime[MAX_SIZE] = {0};

    // Simulate LRU page replacement algorithm
    for (int i = 0; i< n; i++) {
        int page = pages[i];
        int pageFound = 0;

        // Check if the page is already in the frame
        for (int j = 0; j <frameSize; j++) {
            if (frame[j] == page) {
pageFound = 1;
lastUsedTime[page] = i + 1; // Update the last used time of the page
                break;
            }
        }

        // If the page is not in the frame, replace the least recently used page and update the frame
        if (!pageFound) {
            int minTime = n + 1; // Initialize to a large value
            int replaceIndex = -1;

            // Find the least recently used page in the frame
            for (int j = 0; j <frameSize; j++) {
                if (lastUsedTime[frame[j]] <minTime) {
minTime = lastUsedTime[frame[j]];
replaceIndex = j;
                }
            }

            int replacedPage = frame[replaceIndex];
            frame[replaceIndex] = page;
lastUsedTime[page] = i + 1; // Update the last used time of the new page
pageFaults++;

            // Display the current state of the frame after each page replacement
printf("Page Fault %d: Page %d replaces Page %d in frame [", pageFaults, page, replacedPage);
            for (int k = 0; k <frameSize; k++) {
printf("%d", frame[k]);
                if (k <frameSize - 1) {
printf(", ");
                }
            }
printf("]\n");
        }
    }

    // Display the total number of page faults
printf("Total Page Faults: %d\n", pageFaults);

    return 0;
}

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About C

C language is one of the most popular general-purpose programming language developed by Dennis Ritchie at Bell laboratories for UNIX operating system. The initial release of C Language was in the year 1972. Most of the desktop operating systems are written in C Language.

Key features:

  • Structured Programming
  • Popular system programming language
  • UNIX, MySQL and Oracle are completely written in C.
  • Supports variety of platforms
  • Efficient and also handle low-level activities.
  • As fast as assembly language and hence used as system development language.

Syntax help

Loops

1. If-Else:

When ever you want to perform a set of operations based on a condition if-else is used.

if(conditional-expression) {
   // code
} else {
   // code
}

You can also use if-else for nested Ifs and if-else-if ladder when multiple conditions are to be performed on a single variable.

2. Switch:

Switch is an alternative to if-else-if ladder.

switch(conditional-expression) {    
case value1:    
 // code    
 break;  // optional  
case value2:    
 // code    
 break;  // optional  
...    
    
default:     
 // code to be executed when all the above cases are not matched;    
}

3. For:

For loop is used to iterate a set of statements based on a condition.

for(Initialization; Condition; Increment/decrement){  
  // code  
}

4. While:

While is also used to iterate a set of statements based on a condition. Usually while is preferred when number of iterations are not known in advance.

while(condition) {  
 // code 
}

5. Do-While:

Do-while is also used to iterate a set of statements based on a condition. It is mostly used when you need to execute the statements atleast once.

do {
  // code 
} while (condition);

Arrays

Array is a collection of similar data which is stored in continuous memory addresses. Array values can be fetched using index. Index starts from 0 to size-1.

Syntax

One dimentional Array:

data-type array-name[size];

Two dimensional array:

data-type array-name[size][size];

Functions

Function is a sub-routine which contains set of statements. Usually functions are written when multiple calls are required to same set of statements which increases re-usuability and modularity.

Two types of functions are present in C

  1. Library Functions:

Library functions are the in-built functions which are declared in header files like printf(),scanf(),puts(),gets() etc.,

  1. User defined functions:

User defined functions are the ones which are written by the programmer based on the requirement.

How to declare a Function

return_type function_name(parameters);

How to call a Function

function_name (parameters)

How to define a Function

return_type function_name(parameters) {  
  //code
}