Help! Structures, Pointers (Code included)

[raichanh]

Help! Program doesn't crash but the data doesn't seem to save in the structure nor it can be displayed adequately (assuming the data is saved to the structure)

Program for creating a student record of up to ten studentsjust a partial part; I actually suspect that there is something wrong with my pointers)
note that I am trying to make an array of structures:

#include<stdio.h>
#include<string.h>
        
typedef struct str{
        char *name[50];//array of structure of variables
        char *studnum[11];
        int *age;
        float *GWA;
        }studRec;
        
void AddStud(int n){
     studRec tch[10];
                printf("Name:");
                scanf("%s", tch[n].name);
                printf("Student Number:");
                scanf("%s", tch[n].studnum);
                printf("Age:");
                scanf("%d", &tch[n].age);
                printf("GWA:");
                scanf("%f", &tch[n].GWA);}

[quzah]

You just have a bunch of pointers, not any actual data.

struct foo
{
    char name[50]; /* 50 characters for a name */
    char studnum[11] /* 11 characters for num */
    int age; /* an int */
    ...etc...
};

Lose all those * you have there. Then do:

scanf( "%d", &mystructarray[ arrayspot ].age );

Quzah.

[raichanh]

Thanks for the suggestion. Tried doing so, up to no avail.
WHole code:

#include<stdio.h>
#include<string.h>
        
typedef struct str{
        char name[50];//array of structure of variables
        char studnum[11];
        int age;
        float GWA;
        }studRec;
        
void AddStud(int n){
     studRec tch[10];
                printf("Name:");
                scanf("%s", tch[n].name);
                printf("Student Number:");
                scanf("%s", tch[n].studnum);
                printf("Age:");
                scanf("%d", &tch[n].age);
                printf("GWA:");
                scanf("%f", &tch[n].GWA);}                   

void ViewStud(int n){
     studRec tch[10];//viewing
                printf("Row Number %d\n", n+1);
                printf("Name:");
                printf("%s", tch[n].name);
                printf("\nStudent Number:");
                printf("%s", tch[n].studnum);
                printf("\nAge:");
                printf("%d", tch[n].age);
                printf("\nGWA:");
                printf("%f", tch[n].GWA);
                printf("\n");
                }
main(){
       int n, x, viewNum, htr, htx, hty, htz, ........r;
       studRec tch[10];
       printf("---STUDENT RECORD---\n");
       for(;;){
       printf("[1] Add Student\n");
       printf("[2] Edit Student\n");
       printf("[3] View Student\n");
       printf("[4] Exit Record\n");
       printf("Enter:");
       scanf("%d", &x);
       switch(x){
       case 1: if(........r==10){
               printf("Memory Full\n");break;}
               else {htz=10-........r;
                 AddStud(htz); ........r++; break;}
       case 2: 
            printf("Enter which to edit:");
            scanf("%d", &hty);
            hty--;
            ViewStud(hty);
            AddStud(hty);
            printf("Updated Record:\n");
            ViewStud(hty); break;
       case 3:  for(;;){
            printf("Choose an option:\n");
            printf("[1] All\n");
            printf("[2] One of them\n");
            printf("[3] Back to main menu\n");
            scanf("%d", &viewNum);
            if(viewNum==1){
                           for(htr=0; htr<10; htr++){
                           ViewStud(htr);}
                           }
            if(viewNum==2){
                           printf("Enter the row number:");
                           scanf("%d", &htx);
                           ViewStud(htx-1);} 
            if(viewNum==3) break;}
       case 4: break;
       default: printf("Invalid; No action allocated so far\n"); break;
       }
       if(x==4) break;}
}

edit: those dots means 'count'. dunno the one with o removed is a profanity. didn't noticed that

[quzah]

void AddStud(int n){
     studRec tch[10];

void ViewStud(int n){
     studRec tch[10];//viewing

Those are two different arrays. They cease to exist when the function call ends.


Quzah.

[raichanh]

Is that so? So..?
It doesn't work when I remove the other arrays, or when I put it outside the functions, orr should I simply put it inside the main function?

Sorry, I am clueless on this one.

[quzah]

A variable declared inside a function only exists while inside that function, and is destroyed when that function returns (unless it's static). You need to have the array in your main function, then pass it as an argument to the functions you want to use it in.

void dostuff( int array[] )
{
    ...do stuff...
}

int main( void )
{
    int array[4];

    dostuff( array );
}

Quzah.

[raichanh]

I see. So how can I declare the array of structures as part of argument?

[quzah]

Just like you would with any other argument.

void somefunction( struct something somename[], int n )
{
    somename[ n ].age = 5;
}

The reason this works is because arrays are passed as pointers. This is why that works, but this doesn't:[code]

void somefunction( struct something somename[], int n )
{
    n = 5;
}

It's legal to assign n a value here, but you'll notice that outside the function, it doesn't keep. That's because the only way a function can update the value of something passed, is if the something that's passed is an address (pointer) which can be used to update the actual object being referenced.

Quzah.

[raichanh]

I wonder how this works:

void somefunction( struct something somename[], int n )
{
    somename[ n ].age = 5;
}

Because I plan to state somename[ n ].age as entered by user in the program, with n separately determined by the program.

But if you mean that 5 becomes the pointer in somename[ n ].age = 5; , then how is the real data entered?

[quzah]

#include<stdio.h>
struct foo { int bar; };
void fill( struct foo array[], int size )
{
    int x;
    for( x = 0; x < size; x++ )
        array[ x ].bar = 5 * x;
}
void show( struct foo array[], int size )
{
    int x;
    for( x = 0; x < size; x++ )
        printf( "%d\n", array[ x ].bar );
}
int main( void )
{
    struct foo x[ 2 ];
    fill( x, 2 );
    show( x, 2 );

    return 0;
}

Quzah.

[raichanh]

EDIT! I really hate to see that the main problem is that I am not returning the values created in the separate functions!!

Ahh. Wait sorry I have not told you something:

when I try editing, the data is saved. could it be related to switch statement?

EDIT: BTW thanks for the explanations about pointers. learned something new