undefined symbol st (student record system) in C - c

Question

When I try to run the following code, it's generating an error:
undefined symbol st
It's showing me an error on option 2 when I try to display full student records.
I'm running it on turbo C++ compiler.
void main()
{
int option, i;
while (5)
{
printf("========== Student Database ==========\n");
printf("--------------------------------------\n");
printf("1. Insert Record\n");
printf("2. Display Record\n");
printf("3. Edit/Update Record\n");
printf("4. Delete a Record\n");
printf("5. Exit\n");
printf("--------------------------------------\n");
printf("Enter Your Choice: ");
scanf("%d",&option);
if(option==1)
{
struct student st[9];
{
printf("\student data");
}
clrscr();
break;
}
else if(option==2)
{
printf("\n===== Displaying Student Information =====\n");
printf("\n Roll No: \t Name \t \t \t Marks \t Mobile Number\n");
for (i = 0; i < 9; ++i)
{
printf("\n %d \t %st \t \t \t %d \t %d\n", st[i].roll, st[i].name, st[i].marks, st[i].number);
}
clrscr();
break;
}
getch();
}

Answer 1

The problem is that your declaration is in the wrong place.
if(option==1)
{
struct student st[9];
...
}
This declaration is only visible inside the if(option==1) clause, but you try and use it inside else if(option == 2)
I'm guessing that you should move the declaration to the start of your program
void main()
{
int option, i;
struct student st[9];
You should read about a couple of concepts that are important when you use variables, scope which is the area of your program where the variable is visiable, and extent which is the time for which you variable exists. Both were wrong in the code you wrote.
There are lots of other errors in your code, but I guess you'll find out about those as you go a long.

Answer 2

struct student st[9]; is confined to the scope of option equal to 1, so st is out scope in the other parts of the if block, hence the compiler diagnostic.
Declare it at the start of main, as you do for option.
Lastly, think about migrating from a Turbo compiler: The standards have moved on considerably since then, and you're only getting yourself into bad habits.

Answer 3

struct student st[9]; is a local variable in the if blocks, that is not available in else block and you try to use it. Move the declaration above the if to make st array available in the both blocks.

Answer 4

It's because of the scope of st. In your code the variable is only valid inside the if block, i.e. it's not available in the else block. Therefore you get a compile error.
Try this instead:
struct student st[9]; // Declare outside the if
if(option==1)
{
// struct student st[9]; Don't do it inside the if