#include <stdio.h> #include <string.h> #define MAX_USERS 100 struct user { char username[20]; char password[20]; char codeword[20]; }; int num_users = 0; struct user users[MAX_USERS]; int find_user_index(char *username) { for (int i = 0; i < num_users; i++) { if (strcmp(users[i].username, username) == 0) { return i; } } return -1; } void add_user() { if (num_users == MAX_USERS) { printf("Error: maximum number of users reachedn"); return; } struct user u; printf("Enter username: "); scanf("%s", u.username); printf("Enter password: "); scanf("%s", u.password); printf("Enter codeword: "); scanf("%s", u.codeword); users[num_users++] = u; } void edit_user() { char username[20]; printf("Enter username to edit: "); scanf("%s", username); int i = find_user_index(username); if (i == -1) { printf("Error: user not foundn"); return; } struct user u = users[i]; printf("Enter new password (or press enter to keep current password): "); scanf("%s", u.password); printf("Enter new codeword (or press enter to keep current codeword): "); scanf("%s", u.codeword); users[i] = u; } void display_users() { printf("%-20s %-20s %-20sn", "Username", "Password", "Codeword"); for (int i = 0; i < num_users; i++) { printf("%-20s %-20s %-20sn", users[i].username, users[i].password, users[i].codeword); } } void remove_user() { char username[20]; printf("Enter username to remove: "); scanf("%s", username); int i = find_user_index(username); if (i == -1) { printf("Error: user not foundn"); return; } for (int j = i; j < num_users - 1; j++) { users[j] = users[j + 1]; } num_users--; } int main() { int choice; while (1) { printf("n"); printf("1. Add usern"); printf("2. Edit usern"); printf("3. Display usersn"); printf("4. Remove usern"); printf("5. Exitn"); printf("Enter choice: "); scanf("%d", &choice); switch (choice) { case 1: add_user(); break; case 2: edit_user(); break; case 3: display_users(); break; case 4: remove_user(); break; case 5: return 0; default: printf("Error: invalid choicen"); } } } Based on the code above, provide the necessary comments in the code..

1. #include <stdio.h>
#include <string.h>
#define MAX_USERS 100
struct user {
char username[20];
char password[20];
char codeword[20];
};
int num_users = 0;
struct user users[MAX_USERS];
int find_user_index(char *username) {
for (int i = 0; i < num_users; i++) {
if (strcmp(users[i].username, username) == 0) {
return i;
}
}
return -1;
}
void add_user() {
if (num_users == MAX_USERS) {
printf("Error: maximum number of users reachedn");
return;
}
struct user u;
printf("Enter username: ");
scanf("%s", u.username);
printf("Enter password: ");
scanf("%s", u.password);
printf("Enter codeword: ");
scanf("%s", u.codeword);
users[num_users++] = u;
}
void edit_user() {
char username[20];
printf("Enter username to edit: ");
scanf("%s", username);
int i = find_user_index(username);
if (i == -1) {
printf("Error: user not foundn");
return;
}
struct user u = users[i];

2. printf("Enter new password (or press enter to keep current password): ");
scanf("%s", u.password);
printf("Enter new codeword (or press enter to keep current codeword): ");
scanf("%s", u.codeword);
users[i] = u;
}
void display_users() {
printf("%-20s %-20s %-20sn", "Username", "Password", "Codeword");
for (int i = 0; i < num_users; i++) {
printf("%-20s %-20s %-20sn", users[i].username, users[i].password, users[i].codeword);
}
}
void remove_user() {
char username[20];
printf("Enter username to remove: ");
scanf("%s", username);
int i = find_user_index(username);
if (i == -1) {
printf("Error: user not foundn");
return;
}
for (int j = i; j < num_users - 1; j++) {
users[j] = users[j + 1];
}
num_users--;
}
int main() {
int choice;
while (1) {
printf("n");
printf("1. Add usern");
printf("2. Edit usern");
printf("3. Display usersn");
printf("4. Remove usern");
printf("5. Exitn");
printf("Enter choice: ");
scanf("%d", &choice);
switch (choice) {
case 1:
add_user();
break;
case 2:

3. edit_user();
break;
case 3:
display_users();
break;
case 4:
remove_user();
break;
case 5:
return 0;
default:
printf("Error: invalid choicen");
}
}
}
Based on the code above, provide the necessary comments in the code.