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Here is my code. I want it to ask me questions in a sequence. But whenever I enter my choice and put my name it didn't allow me to ask further. How to deal with that?
#include <stdio.h>
#include <stdlib.h>
int new_acc();
int main(){
int one=1, two=2, three=3, four=4, five=5, six=6, seven=7, new_account;
printf("-----WELCOME TO THE MAIN MENU-----\n\n");
printf("%d. Create new account\n",one);
printf("Enter you choice: ");
if (scanf("%d",&one)){
new_account = new_acc(); // calling a function
}
return 0;
}
int new_acc(){
int id; char name;
printf("Enter your name: ");
scanf("%c\n",&name);
printf("Enter your ID card number: ");
scanf("%d\n",&id);
return 0;
}
If you typed Enter after typing nubmer for the MAIN MENU, the newline character remains in the buffer.
Then, is is read as the name via %c.
After that, if you typed, for example, alphabet as name, it will prevent it from reading the number id.
To avoid this, you can put a space before %c to have it skip the newline character.
Also you won't be have to skip after reading name and id, so you should remove \n in scanf() after %c and %d for them.
int new_acc(){
int id; char name;
printf("Enter your name: ");
scanf(" %c",&name); /* add space and remove \n */
printf("Enter your ID card number: ");
scanf("%d",&id); /* remove \n */
return 0;
}
By the way, the above code will allow only one alphabet as name.
To support multi-character name (without space character), you should use an array of char and %s with length specified.
int new_acc(){
int id; char name[1024];
printf("Enter your name: ");
scanf(" %1023s",name); /* don't use & here, and size limit is buffer size - 1 (-1 for terminating null character) */
printf("Enter your ID card number: ");
scanf("%d",&id);
return 0;
}
If you want to support name with space characters, you can use %[\n] (read until newline character) instead of %s.
int new_acc(){
int id; char name[1024];
printf("Enter your name: ");
scanf(" %1023[^\n]",name);
printf("Enter your ID card number: ");
scanf("%d",&id);
return 0;
}
Seems like you want to use an object oriented programming paradigm in this. To so do, you should define an "object" with struct and save the new account with that:
#define MAX 50
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
struct Account {
int id;
char name[MAX];
};
struct Account new_acc();
int main(){
int choice;
struct Account new_account;
printf("-----WELCOME TO THE MAIN MENU-----\n\n");
printf("1. Create new account\n");
printf("Enter you choice: ");
scanf("%d",&choice);
switch(choice) {
case 1:
new_account = new_acc();
break;
default:
printf("Not a valid option\n");
return 1;
}
return 0;
}
struct Account new_acc(){
char name[MAX];
int id;
struct Account new;
printf("Enter your name: ");
scanf("%c\n",name);
printf("Enter your ID card number: ");
scanf("%d\n",&id);
strcpy(new.name, name);
new.id = id;
return new;
}
Pay attention because this code is very vulnerable to buffer overflows. Plus, I edited your check for the option in main because scanf returns 1 if reads whatever value successfully.
Use This Code i have modfified a little bit
int new_acc(){
int id; char name[10];
printf("Enter your name: ");
scanf("%s",name);
printf("Enter your ID card number: ");
scanf("%d",&id);
return 0;
}
Could I please have an explanation of what I am doing wrong.The program is for inputting and displaying student details. It must use a structure and have 2 functions; one to capture(which is to be passed by reference) and another to display (which is to be passed by value.
Here is my code:
#include <stdio.h>
struct Students{
int ID;
char name[50];
int age;
char address[100];
char course[30];
} aStudent[5];
void capture(char *name , int *age , char *address, char *course){
int i;
for(i=0; i<5; i++){
aStudent[i].ID = i+1;
printf("\nFor Student number %d:\n",aStudent[i].ID);
printf("Enter Student Name: ");
scanf ("%s", &aStudent[i].name);
printf("Enter Student Age: ");
scanf ("%d", &aStudent[i].age);
printf("Enter Student Address: ");
scanf ("%s", &aStudent[i].address);
printf("Enter Course: ");
scanf ("%s", &aStudent[i].course);
}
}
void display(char name, int age , char address, char course){
int i;
for(i=0; i<5; i++){
printf("\nStudent %d:\n",aStudent[i].ID);
printf("Name: %s\t\tAge: %d\t\tAddress: %s\t\tCourse:
%s",aStudent[i].name, aStudent[i].age, aStudent[i].address,
aStudent[i].course);
printf("\n");
}
}
void main()
{
int option, age;
char name, address, course;
printf("\t...Welcome to the Student Data System...\n\n");
printf("\nPlease Select An Option: \n1. Input Student Data\n2. View
Student Data\n3. Exit Syatem\n\n");
scanf("%d",&option);
switch(option){
case 1:
printf("Enter Student Details:\n");
capture(name, age , address, course);
break;
case 2:
printf("\nDisplaying Information:\n");
display(name, age , address, course);
break;
case 3:
close();
break;
default:
printf("\nSorry, your option is not valid.");
}
}
I have tested a number of times and it's working, but I'm getting these error messages:
Errors are shown for every argumety I've used
Also, is there a way or a line(s) of code i can use to return to the start of the switch when I am done with one of the cases - A "Return to Main Menu"?
First of all, variables you have tried to pass (either by value or by reference) when you are calling the two functions capture() and display(), haven't used anywhere because you are dealing directly with the members of the structure Students when you are capturing or displaying the results.
And the reasons you are getting syntax errors are because the capture() is expecting the addresses of the variables (&name,&age,&address,&course) and you are passing variables (name,age,address,course) themselves. And also you are using,
scanf ("%s", &aStudent[i].name);
instead of
scanf ("%s", aStudent[i].name);
In my opinion instead of making the Structure array global, declaring it inside main function and passing the whole structure array to the capture() as a reference and passing it by value to the display() is better to your objective as you need to use both call by value and reference in your code.
I have edited your code a bit and added the return to main menu option. It works for me and I apologize if my answer is long and hard to understand because this is my first answer in stackoverflow. Thanks!
#include <stdio.h>
struct Students
{
int ID;
char name[50];
int age;
char address[100];
char course[30];
};
void capture(struct Students *aStudent)
{
int i;
for(i=0; i<2; i++)
{
aStudent[i].ID = i+1;
printf("\nFor Student number %d:\n",aStudent[i].ID);
printf("Enter Student Name: ");
scanf ("%s", aStudent[i].name);
printf("Enter Student Age: ");
scanf ("%d", &aStudent[i].age);
printf("Enter Student Address: ");
scanf ("%s", aStudent[i].address);
printf("Enter Course: ");
scanf ("%s", aStudent[i].course);
}
}
void display(struct Students aStudent[])
{
int i;
for(i=0; i<2; i++)
{
printf("\nStudent %d:\n",aStudent[i].ID);
printf("Name: %s\t\tAge: %d\t\tAddress: %s\t\tCourse: %s",aStudent[i].name, aStudent[i].age, aStudent[i].address,aStudent[i].course);
printf("\n");
}
}
void main()
{
struct Students aStudent[2];
int option;
char choice = 'Y';
printf("\t...Welcome to the Student Data System...\n\n");
while(choice == 'Y' || choice == 'y')
{
printf("\nPlease Select An Option: \n1. Input Student Data\n2. View Student Data\n3. Exit Syatem\n\n");
scanf("%d",&option);
switch(option)
{
case 1:
printf("Enter Student Details:\n");
capture(aStudent);
printf("Return to main menu? (Y/N) :");
scanf(" %c",&choice);
break;
case 2:
printf("\nDisplaying Information:\n");
display(aStudent);
printf("Return to main menu? (Y/N) :");
scanf(" %c",&choice);
break;
case 3:
close();
break;
default:
printf("\nSorry, your option is not valid.");
}
}
}
You have not initialized your string instead you have initialized a character! char name, address, course; If you have used 'char *name, *address, *course;' or char name[100], address[100], course[100]; you might have got the answer ! If you use the above case you should scan using scanf("%s",name); ! Hope I answered your question !
this is the whole code of what im doing, im trying to create a song library that will put what the user enter into file. now the compiler says that passing argument 2 of strcpy makes pointer from integer without a cast and i dont know why. also can u check my linked list for the struct. im so noob at linked list :(
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
struct node {
//definition of struct node to create struct node song
int SongID;
char Title[100];
char Artist[100];
char Composer[100];
char Album[100];
char Genre[100];
int Rating;
char Remarks[1000];
struct node*next;
};
add_song(int SongID, char Title, char Artist, char Composer, char Album, char Genre, int Rating, char Remarks) {
//this is the add song function as stated in the mp2 specs
FILE*fp;
fp=fopen("song.txt","r+");
int i=1, j, choice;
struct node* temp=malloc(sizeof(struct node));
temp->SongID=SongID;
fprintf(fp,"%d",SongID);
strcpy(temp->Title, Title);
fprintf(fp,"%s",Title);
strcpy(temp->Artist, Artist);
fprintf(fp,"%s",Artist);
strcpy(temp->Composer, Composer);
fprintf(fp,"%s",Composer);
strcpy(temp->Album, Album);
fprintf(fp,"%s",Album);
strcpy(temp->Genre, Genre);
fprintf(fp,"%s",Genre);
temp->Rating=Rating;
fprintf(fp,"%d",Rating);
strcpy(temp->Remarks, Remarks);
fprintf(fp,"%s",Remarks);
fclose(fp);
}
int main ()
{
struct node song;
int choice;
int k, i;
int SongID;
char Title[100];
char Artist[100];
char Composer[100];
char Album[100];
char Genre[100];
int Rating;
char Remarks[1000];
/* do
{
printf("Enter 1 to add song, 2 to update song, or 3 to list songs: ");
scanf("%d\n", &choice1);
if (choice1==1)
{*/
srand(time(NULL));
song.SongID=rand();
printf("Enter Title: ");
fgets(Title,100,stdin);
printf("Enter Artist: ");
fgets(Artist,100,stdin);
printf("Enter Composer: ");
fgets(Composer,100,stdin);
printf("Enter Album: ");
fgets(Album,100,stdin);
//for easier code, numbers are being chosen as input
printf("Press 1 for Art Music, 2 for Popular Music, or 3 for Traditional Music): ");
scanf("%d", &choice);
if (choice==1)
{
strcpy(song.Genre,"Art Music");
}
else if (choice==2)
{
strcpy(song.Genre,"Popular Music");
}
else if (choice==3)
{
strcpy(song.Genre,"Traditional Music");
}
else
{
printf("You entered a blank genre.\n");
}
printf("Enter your rating, choose from 1-5: ");
scanf("%d", &Rating);
printf("Enter Remarks: ");
fgets(Remarks,1000,stdin);
add_song(SongID, Title, Artist, Composer, Album, Genre, Rating, Remarks);
/*k=0;
break;
}
else if (choice1==2)
{
//update_song(song);
k=0;
break;
}
else if (choice1==3)
{
// list_songs(song);
k=0;
break;
}
else
{
k=1;
printf("That is not a valid input.\n");
}
}while (k==1);*/
return 0;
}
Your function definition don't match with the arguments you pass. It should be
void add_song(int SongID, char *Title, char *Artist, char *Composer, \
char *Album, char *Genre, int Rating, char *Remarks) {
...
...
}
Another issue is that songID is uninitialized in main(). Reading from an uninitialized variable is undefind behaviour.
Another problem you might face is that fgets() reads the newline \n into buffer if there's space available which might be problematic.
Something to be aware of and you need trim it if nececcary.
This is working copy of your code except one thing "Remark". Before executing scanf for Remark process exits . Change your arguments as I did here and also change fopen mode as +w so if file is not exist it can be created automatically. strcpy prototype is `char *strcpy(char *dest, const char *src).
So I have changed accordingly
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
struct node {
//definition of struct node to create struct node song
int SongID;
char Title[100];
char Artist[100];
char Composer[100];
char Album[100];
char Genre[100];
int Rating;
char Remarks[1000];
struct node *next;
};
void add_song(int SongID, char *Title, char *Artist, char *Composer, char *Album, char *Genre, int Rating, char *Remarks) {
//this is the add song function as stated in the mp2 specs
FILE *fp;
fp=fopen("song.txt","a+");
int i=1, j, choice;
struct node* temp=malloc(sizeof(struct node));
temp->SongID=SongID;
fprintf(fp,"%d",SongID);
strcpy(temp->Title, Title);
fprintf(fp,"%s",Title);
strcpy(temp->Artist, Artist);
fprintf(fp,"%s",Artist);
strcpy(temp->Composer, Composer);
fprintf(fp,"%s",Composer);
strcpy(temp->Album, Album);
fprintf(fp,"%s",Album);
strcpy(temp->Genre, Genre);
fprintf(fp,"%s",Genre);
temp->Rating=Rating;
fprintf(fp,"%d",Rating);
strcpy(temp->Remarks, Remarks);
fprintf(fp,"%s",Remarks);
fclose(fp);
}
int main ()
{
struct node song;
int choice;
int k, i;
int SongID;
char Title[100];
char Artist[100];
char Composer[100];
char Album[100];
char Genre[100];
int Rating;
char Remarks[1000];
/* do
{
printf("Enter 1 to add song, 2 to update song, or 3 to list songs: ");
scanf("%d\n", &choice1);
if (choice1==1)
{*/
srand(time(NULL));
song.SongID=rand();
printf("Enter Title: ");
fgets(Title,100,stdin);
printf("Enter Artist: ");
fgets(Artist,100,stdin);
printf("Enter Composer: ");
fgets(Composer,100,stdin);
printf("Enter Album: ");
fgets(Album,100,stdin);
//for easier code, numbers are being chosen as input
printf("Press 1 for Art Music, 2 for Popular Music, or 3 for Traditional Music): ");
scanf("%d", &choice);
if (choice==1)
{
strcpy(song.Genre,"Art Music");
}
else if (choice==2)
{
strcpy(song.Genre,"Popular Music");
}
else if (choice==3)
{
strcpy(song.Genre,"Traditional Music");
}
else
{
printf("You entered a blank genre.\n");
}
printf("Enter your rating, choose from 1-5: ");
scanf("%d",&Rating);
printf("Enter Remarks: \n");
fgets(Remarks,1000,stdin);
add_song(SongID, Title, Artist, Composer, Album, Genre, Rating, Remarks);
/*k=0;
break;
}
else if (choice1==2)
{
//update_song(song);
k=0;
break;
}
else if (choice1==3)
{
// list_songs(song);
k=0;
break;
}
else
{
k=1;
printf("That is not a valid input.\n");
}
}while (k==1);*/
return 0;
}
Didn't go through the whole code, but strcpy problem is obvious. According to definition of function strcpy (http://www.tutorialspoint.com/c_standard_library/c_function_strcpy.htm), it expects two char pointers (aka strings in C)
char *strcpy(char *dest, const char *src)
You're passing only char arguments to a function add_song, which is just not the pointer. Change the signature of the function add_song and then you should be fine with strcpy
I was practicing array of structure. I made the following program and there were no compiling errors.But when i try to run it(I guess these errors are called runtime errors?),it stops working just after accepting the roll number. I wonder what wrong i did.
I use Dev c++ and gcc compiler.
Here's the code:
#include<stdio.h>
struct student{
char Fname[];
char Lname[];
int reg_no;
int Class;
char sec;
};
void enterinfo(student *,int);
void Display(student *,int);
int main()
{
int i;
printf("\t\t\t Enter student's information\n\n\n\n");
printf("How many students are there in you're school: ");
scanf("%d",&i);
student ob[i],*ptr;
ptr=ob;
enterinfo(ptr,i);
Display(ptr,i);
}
void enterinfo(student *e,int y)
{
char CONT='y';
for (int j=0;j<y && (CONT=='y' || CONT=='Y');j++)
{
printf("Enter Students First Name: ");
scanf("%s",e->Fname);
printf("Enter Students Last Name: ");
scanf("%s",e->Lname);
printf("Enter Roll number: ");
scanf("%d",e->reg_no);
printf("Enter class: ");
scanf("%d",e->Class);
printf("Enter Section: ");
scanf("%d",e->sec);
printf("\n\n\n\n Do you want to enter more? : ");
scanf("%c",&CONT);
}
}
void Display(student *e,int y)
{
char CONT='y';
for (int j=0;j<y;j++)
{
printf("Students name : %s %s",e->Fname,e->Lname);
printf("Enter Roll number: %d",e->reg_no);
printf("class: %d",e->Class);
printf("Enter Section: %d",e->sec);
}
}
I've made the following changes to your code and it started working for me:
char Fname[]; --> char Fname[100];
char Lname[]; --> char Lname[100];
char sec; --> int sec; This is needed for scanf.
scanf("%d",e->reg_no); --> scanf("%d",&e->reg_no);
scanf("%d",e->Class); --> scanf("%d",&e->Class);
scanf("%d",e->sec); --> scanf("%d",&e->sec);
adding \n to the end of printf strings in Display
Please note that scanf("%s", ...) is insecure and it can cause a crash the input string is longer than the array size you're reading it to, i.e. if the user types a name of at least 100 bytes.
Please note that you should always check the return value of scanf, and abort early on error (i.e. if it doesn't return 1 in your case).
Please note that in C++ the istream methods (http://en.cppreference.com/w/cpp/header/istream) provide a safer way to read the input.
Here:
scanf("%d",e->reg_no);
you should insert a '&' symbol before e->reg_no. But I can see many other problems once you solve this...
You can use below code, it will run on both linux & windows. Your program halts because of:
scanf("%d",&e->reg_no);
printf("Enter class: ");
scanf("%d",&e->Class);
printf("Enter Section: ");
scanf("%d",&e->sec);
you did not use & which is must for int, char, float data types as it is used as reference of the variable.
#include
struct student{
char Fname[30];
char Lname[30];
int reg_no;
int Class;
char sec[5];
};
void enterinfo(student *,int);
void Display(student *,int);
int main()
{
int i;
printf("\t\t\t Enter student's information\n\n\n\n");
printf("How many students are there in you're school: ");
scanf("%d",&i);
student * ob = new student[i];
enterinfo(ob,i);
Display(ob,i);
}
void enterinfo(student *e,int y)
{
char CONT='y';
for (int j=0;jFname);
printf("Enter Students Last Name: ");
scanf("%s",e->Lname);
printf("Enter Roll number: ");
scanf("%d",&e->reg_no);
printf("Enter class: ");
scanf("%d",&e->Class);
printf("Enter Section: ");
scanf("%s",e->sec);
getchar();//to eat newline/ enter char of previous statement
printf("\n\n\n\n Do you want to enter more? : ");
scanf("%c",&CONT);
}
}
void Display(student *e,int y)
{
for (int j=0;jFname,e->Lname);
printf("\nEnter Roll number: %d",e->reg_no);
printf("\nclass: %d",e->Class);
printf("\nEnter Section: %s\n",e->sec);
}
}
I have made a program which is a small library operated via software. When I add two books and then delete the first book the second book gets the same bookid as the first book because of count-- in the del() function. I cannot rely on printing the count as the bookid. Is there a better option?
#include<stdio.h>
#include<conio.h>
#include<stdlib.h>
static int count;
struct book
{
int bookid;
char name[30];
char author[30];
float price;
};
struct book b[40];
void add(void);
void del(void);
void sort(void);
void price(void);
void print(void);
void main(void)
{
char choice;
while(1)
{
clrscr();
printf("Enter a choice:\n 1.Add a book.\n 2.Delete a book.\n 3.Sort books by price.\n 4.To print all books details.\n 5.To print the names of the books whose price is less than 1000.\n 6.Exit\n");
choice=getche();//doing by getch() as getche makes the program rough as it is printed
switch(choice)
{
case'1':add();break;
case'2':del();break;
case'3':sort();break;
case'4':print();break;
case'5':price();break;
case'6':exit(0);
default:printf("Enter a valid choice.");break;
}
}/*switch ends*/
}
void add(void)
{
int i;
char ch[30];
clrscr();
for(i=count;i<40;i++)
{
printf("Enter books name:\n");
gets(b[i].name);
printf("Enter author's name\n");
gets(b[i].author);
printf("Enter price:\n");
gets(ch);
b[i].price=atoi(ch);
printf("Dear User,the book has succesfully been added.The book id is %d",i);
count++;
break;
} /* for ends*/
getch();
}
void print(void)
{
int i;
clrscr();
for(i=0;i<count;i++)
{
printf("Bookid=%d,Name=%s,Author=%s,Price=%f\n",b[i].bookid,b[i].name,b[i].author,b[i].price);
}
getch();
}
void del(void)
{
int i,j;
char ch[10];
clrscr();
printf("Enter book id:");
gets(ch); // how do i put it into the structure as i dont know that which structure it belongs to
for(i=0;i<count;i++) //searching
{
if(b[i].bookid==atoi(ch))
{
for(j=i;j<count;j++)
{
b[j]=b[j+1];
}//for j ends
} //if ends
} /* for of i ends */
count--;
getch();
}
//void del(void)
//{
// int i;
// char ch[10];
// clrscr();
//printf("Enter book id:");
// gets(ch);
// for(i=0;i<40;i++)
// {
// b[i]=b[i+1];
//
// }
// count--;
// printf("Dear user,delete succesful");
//getch();
//}
void sort(void)
{
int i;
float temp;
for(i=0;i<40;i++)
{
if(b[i].price>b[i+1].price)
{
temp=b[i].price;
b[i].price=b[i+1].price;
b[i+1].price=temp;
}
}/*for ends*/
printf("Dear user,the books are sorted by price.\n");
getch();
}
void price(void)
{
int i;
clrscr();
for(i=0;i<count;i++)
{
if(b[i].price<1000)
{
printf("%d.%s\n",i+1,b[i].name);
}
}
getch();
}
One way is to have two global counters: one has the number of books stored, the other gives the next (unique) book id, as Tyler McHenry points out. When you delete a book, decrement the number of books, but never decrement the next book id.
I notice that when a book is deleted, you move the rest of the book entries together ("compress" them) so your array is always "dense". So another solution is to add a "deleted" flag to the book structure. Now you don't compress the entries when a book is deleted, but when a book is added, the code must search for an empty place in the array. Also the bookid is just the position in the array. (By the way, if you hard-code sizes, like the size of an array, do it once.)
#define MAXSTR (30)
struct book
{
int bookid;
int valid; // 1 is valid, 0 is empty or deleted
char name[MAXSTR];
char author[MAXSTR];
float price;
};
#define MAXBOOKS (40)
struct book b[MAXBOOKS];
int findEmpty()
{
int i;
for (i=0; i < MAXBOOKS; i++) {
if (! b[i].valid) return i;
}
return -1; // no more space
}
void add(void)
{
int i = findEmpty();
char ch[MAXSTR];
if (i < 0) return; // no room for more books
clrscr();
printf("Enter books name:\n");
fgets(b[i].name, MAXSTR, stdin);
printf("Enter author's name\n");
fgets(b[i].author, MAXSTR, stdin);
printf("Enter price:\n");
fgets(ch, MAXSTR, stdin);
b[i].price=atoi(ch);
/* Assign the empty location found to this book */
b[i].bookid = i;
/* mark that it is valid */
b[i].valid = 1;
printf("Dear User,the book has succesfully been added.The book id is %d", b[i].bookid);
getch();
}
del() now just marks the book as invalid. The main part of del() looks like this.
gets(ch);
int idToDelete = atoi(ch);
// find which structure it belongs to
for(i=0;i
Use a selection sort in sort() instead of the one-pass routine (which doesn't work in all cases) which is there. Printing books should skip any book that is not valid, too.
some pointers:
use fgets instead of gets, its safer
because you can specify max buf len
in add() there is no book id assigned,
so it will - due to being global -
remain 0
why do u need book id? you
have an array of 40, use the array
index as id.
Your first problem seems to be that you are never actually setting the bookid field of the book structure to anything. It will end up having some arbitrary value in each book struct, which will make it pure luck if del ever works correctly.
Your problem is in here:
printf("Enter books name:\n");
gets(b[i].name);
printf("Enter author's name\n");
gets(b[i].author);
printf("Enter price:\n");
gets(ch);
b[i].price=atoi(ch);
printf("Dear User,the book has succesfully been added.The book id is %d",i);
count++;
Take a look at this code, and show me where you set the value of b[i].bookid. The answer is nowhere. So try changing the last few lines to:
b[i].bookid = i;
printf("Dear User,the book has succesfully been added.The book id is %d", b[i].bookid);
count++;
Now, this still has a problem if you ever call add after calling del, because in the single-iteration loop that that code is in, i is always set to count. So, as you noticed, if count ever changes, which it will frequently, you will assign duplicate IDs. One solution is to define, at the top of the add function, a static variable (which retains its value between calls to the function) indicating what the next book id should be, like so:
void add(void)
{
static int nextBookId = 0;
int i = count;
char ch[30];
/* Do not overrun the array */
if (count >= 40) return;
clrscr();
printf("Enter books name:\n");
gets(b[i].name);
printf("Enter author's name\n");
gets(b[i].author);
printf("Enter price:\n");
gets(ch);
b[i].price=atoi(ch);
/* Assign the next unique book ID to this book, then increment nextBookId,
which will retain its incremented value next time you call add() */
b[i].bookid = nextBookId++;
printf("Dear User,the book has succesfully been added.The book id is %d", b[i].bookid);
count++;
getch();
}
Note that I replaced your loop with a simple bounds check at the top.
This way, every book you add gets its own, unique identifier that does not necessarily correspond to its position in the array or the number of books that existed at the time it was added. This method will not re-use IDs of previously deleted books, but that is probably a desirable behavior.