How replace a string of a specific person in a file - c

Question

I'm having a bit of problem. I've set the string 'Absent' to all student in a file. However, I want to replace 'Absent' with 'present' when the correct ID assigned to a student is entered. In other words, 'Absent' will only change to 'Present' for a specific person at a time. I'm not sure how to implement this and I'm asking kindly if someone would help. Thanks in advance.
UPDATE::====
#include <stdio.h>
#include <conio.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>
#include <time.h>
#include <errno.h>
typedef struct record {
char *fname;
char *lname;
int code;
char *stat;
} information;
int main (void) {
int i;
char ffname[28], flname[28], ans, status[15];
int fID, j, id_, x;
FILE *kfile, *ufile;
x = 0;
j = 0;
i = 0;
char buf[150];
time_t curtime;
struct tm* loc_time;
information array[100];
printf(" **********Attendance Recording System**********\n");
printf(" MENU \n");
//Getting current time of system
curtime = time (NULL);
// Converting current time to local time
loc_time = localtime (&curtime);
strftime (buf,150, "%I:%M %p.\n", loc_time);
//prints error message if file cannot be found within the system
if ((kfile = fopen("information.txt", "r")) == NULL) //If the file path is incorrect, an error message is displayed
{
fprintf(stderr, "Error while opening file (%d: %s)\n",errno, strerror(errno)); //Error message that will be displayed if file path is incorrect
return;
}
//while the file is opened and not at the end, the strings are stored into variables which forms an array of strings
for (x = 0; x < 200; x++) {
if (fscanf(kfile, "%s %s %d", ffname, flname, &fID) != 3) //Reads the contents of the file
break;
array[x].fname = strdup(ffname);
array[x].lname = strdup(flname);
array[x].code = fID;
}
fclose(kfile);
ufile= fopen("update.txt","w");
strcpy(status, "Absent");
fprintf(ufile,"First Name Last Name ID Status Time Arrived\n");
for (i = 0; i < x; i++) {
fprintf(ufile,"%-15s%-14s%2d%12s ",(array[i].fname), (array[i].lname), (array[i].code), status);
fprintf(ufile,"%16s",(buf));
}
fclose(ufile);
while(j < x){
printf("Enter you ID: ");
scanf("%d", &id_);
strcpy(status, "Absent");
bool isPresentInFile = false;
for(i=0; i<x; i++)
{
if(array[x].code == id_)
{
printf(" %s %s?", array[x].fname, array[x].lname);
isPresentInFile = true;
break;
}
}
if(isPresentInFile)
{
strcpy(status, "present");
}
j++;
}
fprintf(ufile,"First Name Last Name ID Status Time Arrived\n");
for (i = 0; i < x; i++) {
fprintf(ufile,"%-15s%-14s%2d%12s ",(array[i].fname), (array[i].lname), (array[i].code), status);
fprintf(ufile,"%16s",(buf));
}
fclose(ufile);
getch();
return 0;
}
UPDATE #3
#include <stdio.h>
#include <conio.h>
#include <stdlib.h>
#include <string.h>
#include <stdbool.h>
#include <time.h>
#include <errno.h>
typedef struct record {
char *fname;
char *lname;
int code;
} information;
int main (void) {
int i;
char ffname[28], flname[28], ans, ans1, status[15];
int fID, j, id_, x;
FILE *kfile, *ufile;
x = 0;
j = 0;
i = 0;
char buf[150];
time_t curtime;
struct tm* loc_time;
information array[100];
printf(" **********Attendance Recording System**********\n");
printf(" MENU \n");
//Getting current time of system
curtime = time (NULL);
// Converting current time to local time
loc_time = localtime (&curtime);
strftime (buf,150, "%I:%M %p.\n", loc_time);
//prints error message if file cannot be found within the system
if ((kfile = fopen("information.txt", "r")) == NULL) //If the file path is incorrect, an error message is displayed
{
fprintf(stderr, "Error while opening file (%d: %s)\n",errno, strerror(errno)); //Error message that will be displayed if file path is incorrect
return;
}
//while the file is opened and not at the end, the strings are stored into variables which forms an array of strings
for (x = 0; x < 200; x++) {
if (fscanf(kfile, "%s %s %d", ffname, flname, &fID) != 3) //Reads the contents of the file
break;
array[x].fname = strdup(ffname);
array[x].lname = strdup(flname);
array[x].code = fID;
}
fclose(kfile);
while(j < x){
Next:
printf("Enter you ID: ");
scanf("%d", &id_);
strcpy(status, "Absent");
bool isPresentInFile = false;
for(i=0; i<x; i++)
{
if(array[i].code == id_)
{
printf("Are you %s %s?", array[i].fname, array[i].lname);
printf("\n");
printf("[y/n only]: ");
scanf(" %c", &ans);
isPresentInFile = true;
break;
}//end of if statement
}//end of for loop
if(isPresentInFile)
{
strcpy(status, "present");
}//end of if statement
switch (ans){
case 'y':
ufile= fopen("update.txt","w");
fprintf(ufile,"First Name Last Name ID Status Time Arrived\n");
for (i = 0; i < x; i++) {
fprintf(ufile,"%-15s%-14s%2d%12s ",(array[i].fname), (array[i].lname), (array[i].code), status);
fprintf(ufile,"%16s",(buf));
}//end of for loop
fclose(ufile);
printf("Continue?\n");
printf("[y/n]: ");
scanf(" %c", &ans1);
if(ans1 == 'y'){
break;
}//end of if statements
else if (ans1 == 'n'){
exit(EXIT_SUCCESS);
}//end of else statement to check if ans1 is equal to 'n'
case 'n':
goto Next;
break;
default:
printf("invalid entry. Try again");
}//end of switch case statememt
j++;
}//end of while
getch();
return 0;
}

Answer 1

From your question, I didn't get when exactly do you want to change status from "Absent" to "present".
But you can use the same strcpy() method to overwrite your status variable.
...
strcpy(status, "Absent");
if(//condition)
{
strcpy(status, "present");
}
UPDATE 1:
After reading your comment, I understood that you will prompt the user to enter an ID. And if it matches with the ID present in the file, you need to update the status to "present" and then write to the new file.
I can think of something like this:
...
// read from file
.....
int ID;
printf("Enter you ID: ");
scanf("%d", &ID);
strcpy(status, "Absent");
bool isPresentInFile = false;
for(int i=0; i<x; ++i)
{
if(array[x].code == ID)
{
isPresentInFile = true;
break;
}
}
if(isPresentInFile)
{
strcpy(status, "present");
}
...
// write to file
.....
UPDATE 2:
After reading the updated question, I notice that you are writing to the file at the end! But overwriting the status variable each time. This way you end up writing either "Absent" or "Present" for all the entries in the file (Note that it pertains to the last candidate who enters his ID!)
To avoid this, do either of the following:
Write to the file as soon as you know the status of a candidate.
while(j < x)
{
printf("Enter you ID: ");
scanf("%d", &id_);
strcpy(status, "Absent");
bool isPresentInFile = false;
for(i=0; i<x; i++)
{
if(array[x].code == id_)
{
printf(" %s %s?", array[x].fname, array[x].lname);
isPresentInFile = true;
break;
}
}
if(isPresentInFile)
{
strcpy(status, "present");
}
// write to file here
j++;
}
Also have a field called status in the structure information.
By default, keep it "Absent" for all the candidates.
Then make it "Present" only for those who enter their IDs. Finally, write it to the file.