#include <stdio.h>
#include <stdlib.h>
#include <string.h>
 
struct Employee {
    int id;
    char name[50];
    float basicSalary;
    float hra, da, gross;
};
 
// Function to calculate gross salary
float calculateGross(struct Employee *e) {
    e->hra = e->basicSalary * 0.20;
    e->da = e->basicSalary * 0.10;
    e->gross = e->basicSalary + e->hra + e->da;
    return e->gross;
}
 
// Function to add employee record
void addEmployee() {
    FILE *fp;
    struct Employee e;
    fp = fopen("payroll.dat", "ab"); // append binary mode
    if (!fp) {
        printf("Error opening file!\n");
        return;
    }
 
    printf("\nEnter Employee ID: ");
    scanf("%d", &e.id);
    printf("Enter Name: ");
    scanf("%s", e.name);
    printf("Enter Basic Salary: ");
    scanf("%f", &e.basicSalary);
 
    calculateGross(&e);
    fwrite(&e, sizeof(e), 1, fp);
    fclose(fp);
    printf("Employee added successfully!\n");
}
 
// Function to display all employee records
void displayEmployees() {
    FILE *fp;
    struct Employee e;
    fp = fopen("payroll.dat", "rb");
    if (!fp) {
        printf("Error opening file!\n");
        return;
    }
 
    printf("\n--- Employee Payroll Records ---\n");
    printf("%-10s %-15s %-12s %-10s %-10s %-10s\n",
           "ID", "Name", "Basic", "HRA", "DA", "Gross");
 
    while (fread(&e, sizeof(e), 1, fp)) {
        printf("%-10d %-15s %-12.2f %-10.2f %-10.2f %-10.2f\n",
               e.id, e.name, e.basicSalary, e.hra, e.da, e.gross);
    }
 
    fclose(fp);
}
 
// Function to search employee by ID
void searchEmployee() {
    FILE *fp;
    struct Employee e;
    int id, found = 0;
 
    fp = fopen("payroll.dat", "rb");
    if (!fp) {
        printf("Error opening file!\n");
        return;
    }
 
    printf("Enter Employee ID to search: ");
    scanf("%d", &id);
 
    while (fread(&e, sizeof(e), 1, fp)) {
        if (e.id == id) {
            printf("\nEmployee Found!\n");
            printf("ID: %d\nName: %s\nBasic: %.2f\nHRA: %.2f\nDA: %.2f\nGross: %.2f\n",
                   e.id, e.name, e.basicSalary, e.hra, e.da, e.gross);
            found = 1;
            break;
        }
    }
 
    if (!found)
        printf("Employee not found!\n");
 
    fclose(fp);
}
 
// Function to update employee record
void updateEmployee() {
    FILE *fp;
    struct Employee e;
    int id, found = 0;
    long pos;
 
    fp = fopen("payroll.dat", "rb+");
    if (!fp) {
        printf("Error opening file!\n");
        return;
    }
 
    printf("Enter Employee ID to update: ");
    scanf("%d", &id);
 
    while (fread(&e, sizeof(e), 1, fp)) {
        if (e.id == id) {
            found = 1;
            pos = ftell(fp) - sizeof(e);
 
            printf("Enter new Basic Salary: ");
            scanf("%f", &e.basicSalary);
            calculateGross(&e);
 
            fseek(fp, pos, SEEK_SET);
            fwrite(&e, sizeof(e), 1, fp);
            printf("Employee record updated!\n");
            break;
        }
    }
 
    if (!found)
        printf("Employee not found!\n");
 
    fclose(fp);
}
 
// Function to delete an employee record
void deleteEmployee() {
    FILE *fp, *temp;
    struct Employee e;
    int id, found = 0;
 
    fp = fopen("payroll.dat", "rb");
    temp = fopen("temp.dat", "wb");
 
    if (!fp || !temp) {
        printf("Error opening file!\n");
        return;
    }
 
    printf("Enter Employee ID to delete: ");
    scanf("%d", &id);
 
    while (fread(&e, sizeof(e), 1, fp)) {
        if (e.id != id)
            fwrite(&e, sizeof(e), 1, temp);
        else
            found = 1;
    }
 
    fclose(fp);
    fclose(temp);
 
    remove("payroll.dat");
    rename("temp.dat", "payroll.dat");
 
    if (found)
        printf("Employee record deleted successfully!\n");
    else
        printf("Employee not found!\n");
}
 
// Main Menu
int main() {
    int choice;
 
    do {
        printf("\n===== Employee Payroll System =====\n");
        printf("1. Add Employee\n");
        printf("2. Display All Employees\n");
        printf("3. Search Employee by ID\n");
        printf("4. Update Employee Salary\n");
        printf("5. Delete Employee\n");
        printf("6. Exit\n");
        printf("Enter your choice: ");
        scanf("%d", &choice);
 
        switch (choice) {
            case 1: addEmployee(); break;
            case 2: displayEmployees(); break;
            case 3: searchEmployee(); break;
            case 4: updateEmployee(); break;
            case 5: deleteEmployee(); break;
            case 6: printf("Exiting...\n"); break;
            default: printf("Invalid choice!\n");
        }
    } while (choice != 6);
 
    return 0;
}