/*
 * C Program to Create Employee Record and Update it
 */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define size 200

struct emp
{
    int id;
    char *name;
}*emp1, *emp3;

void display();
void create();
void update();

FILE *fp, *fp1;
int count = 0;

void main(int argc, char **argv)
{
    int i, n, ch;
    printf("1] Create a Record\n");
    printf("2] Display Records\n");
    printf("3] Update Records\n");
    printf("4] Exit");
    while (1)
        {
            printf("\nEnter your choice : ");
            scanf("%d", &ch);
            switch (ch)
                {
                case 1:
                    fp = fopen(argv[1], "a");
                    create();
                    break;
                case 2:
                    fp1 = fopen(argv[1],"rb");
                    display();
                    break;
                case 3:
                    fp1 = fopen(argv[1], "r+");
                    update();
                    break;
                case 4:
                    exit(0);
                }
        }
}

/* To create an employee record */
void create()
{
    int i;
    char *p;
    emp1 = (struct emp *)malloc(sizeof(struct emp));
    emp1->name = (char *)malloc((size)*(sizeof(char)));
    printf("Enter name of employee : ");
    scanf(" %[^\n]s", emp1->name);
    printf("Enter emp id : ");
    scanf(" %d", &emp1->id);
    fwrite(&emp1->id, sizeof(emp1->id), 1, fp);
    fwrite(emp1->name, size, 1, fp);
    count++;   // count to number of entries of records
    fclose(fp);
}

/* Display the records in the file */
void display()
{
    emp3=(struct emp *)malloc(1*sizeof(struct emp));
    emp3->name=(char *)malloc(size*sizeof(char));
    int i = 1;
    if (fp1 == NULL)
        printf("\nFile not opened for reading");
    while (i <= count)
        {
            fread(&emp3->id, sizeof(emp3->id), 1, fp1);
            fread(emp3->name, size, 1, fp1);
            printf("\n%d %s",emp3->id,emp3->name);
            i++;
        }
    fclose(fp1);
    free(emp3->name);
    free(emp3);
}

void update()
{
    int id, flag = 0, i = 1;
    char s[size];
    if (fp1 == NULL)
        {
            printf("File cant be opened");
            return;
        }
    printf("Enter employee id to update : ");
    scanf("%d", &id);
    emp3 = (struct emp *)malloc(1*sizeof(struct emp));
    emp3->name=(char *)malloc(size*sizeof(char));
    while(i<=count)
        {
            fread(&emp3->id, sizeof(emp3->id), 1, fp1);
            fread(emp3->name,size,1,fp1);
            if (id == emp3->id)
                {
                    printf("Enter new name of emplyee to update : ");
                    scanf(" %[^\n]s", s);
                    fseek(fp1, -204L, SEEK_CUR);
                    fwrite(&emp3->id, sizeof(emp3->id), 1, fp1);
                    fwrite(s, size, 1, fp1);
                    flag = 1;
                    break;
                }
            i++;
        }
    if (flag != 1)
        {
            printf("No employee record found");
            flag = 0;
        }
    fclose(fp1);
    free(emp3->name);        /* to free allocated memory */
    free(emp3);
}