Need help with Single Linked List Database Assignment

I have to write a menu UI program that adds student's name, score, average, letter grade, show all data for 1 particular student, and show all the data. the name has to be a string, id is a string of 4, and score is an int array of 4. The program is to be implemented using linked-list.
This is what I got so far and it's not looking good... We had a similar assignment but using structures instead of linked-lists and I attempted to convert it with no luck :(

Code:

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#include <stdio.h>
#include <windows.h>
#include <stdlib.h>

#define FLUSH while (getchar() != '\n')
#define M 3
#define N 4

typedef struct node *nd;
struct node
{
        char sId[4];
        char name[40];
        int score[N];
        char grade;
        struct node *next;
       
}STUD;

void inputData(nd *head);
void inquireScores(nd head);
void inquireAverage(nd head);
void inquireGrade(nd head);
void inquireStudent(nd head);
void showAll(nd head);
int search(nd head);
void showScore(nd head);
void showName(nd head);
float calcAverage(nd head);
char getGrade(float);
void showError(void);

int main(void)
{
    struct STUD *nd;
    int ans,n;
   
    inputData(&nd);
   
    do{
 
        system("cls");           
        printf("1] Student Score\n");         
        printf("2] Student Average:\n");
        printf("3] Student Grade\n");
        printf("4] Student Academic Record\n");
        printf("5] Student List\n");
        printf("6] Exit\n\n");
        printf("Choice: ");
        scanf("%d",&ans);
        switch(ans)
      {
              case 1:  inquireScores(nd); 
                        break;
              case 2:  inquireAverage(nd);
                        break;
              case 3:  inquireGrade(nd);
                        break;
              case 4:  inquireStudent(nd);
                        break;
              case 5:  showAll(nd);
                        break;
              case 6:  printf("\n\nClosing program...");
                        sleep(3000);
                        break;
              default:  printf("\n\nInvalid choice...");
                        sleep(2000);
        }
    }while (ans != 6);
    return 0;

}

   
void inputData(nd *head)
{
    char sId[4];
    char name[30];
    nd t, t2, temp;
    temp=malloc(sizeof(STUD));
    temp -> next = NULL;
   
    while(temp->next != NULL)   
    {
          t = temp->next;
          t2 = temp->next;
          system("cls");
         
          printf("ID: ");
          strcpy(t->sId, sId);
          printf("\nName: ");
          strcpy(temp->name, name);
          printf("\nscore [%d]: ");
          scanf("%d",&t2->score);
         
          FLUSH;
    }
    return;
}

void showName(nd head)
{
    nd temp;
    temp=malloc(sizeof(STUD));
    temp -> next = NULL;
   
    while(temp->next != NULL)
    {
    system("cls");
    printf("Student ID: %s\n",temp->sId);
    printf("Student Name: %s\n",temp->name);   
    }
    return;
}

void showScore(nd head)
{
    nd temp;
    temp=malloc(sizeof(STUD));
    temp -> next = NULL;
    printf("Scores: \n");
    while(temp->next != NULL)
    {
    printf("    %d\n",temp->score);     
    }
    return;
}

void showError(void)
{
    printf("Student ID not found...");
    getch();
   
    return;
}
 
void inquireScores(nd head)
{
    char name[30];
    nd temp;
    temp=malloc(sizeof(STUD));
    temp -> next = NULL;
   
    while (temp != NULL && strcmp(temp->name, name) != 0)
    {
          temp = temp->next;
    }

    if (temp == NULL)
    {
        showError();
        return;
    }
    else
    {
          showName(head);         
          showScore(head);
          getch();
    }
    return;
}

void inquireAverage(nd head)
{
   
    nd temp;
    char name[30],gr;
    float avg;
    temp=malloc(sizeof(STUD));
    temp -> next = NULL;
   
    while (temp != NULL && strcmp(temp->name, name) != 0)
    {
          temp = temp->next;
    }

    if (temp == NULL)
    {
        showError();
        return;
    }
    else
    {
         
          avg = calcAverage(head);
          showName(head);
          printf("Average: %0.2f",avg);
          getch();
    }
    return;
   
}

void inquireGrade(nd head)
{
      nd temp;
    char name[30],gr;
    float avg;
    temp=malloc(sizeof(STUD));
    temp -> next = NULL;
   
    while (temp != NULL && strcmp(temp->name, name) != 0)
    {
          temp = temp->next;
    }

    if (temp == NULL)
    {
        showError();
        return;
    }
    else
    {
          avg = calcAverage(head);
          gr = getGrade(avg);
          showName(head);
          printf("\nGrade: %c",gr);
          getch();
    }
    return;
}

char getGrade(float avg)
{
    char gr;
   
    if (avg >= 91)
        gr = 'A';
    else if ((gr >= 81) && (gr <= 90))
          gr = 'B';
    else if ((gr >= 71) && (gr <= 80))
          gr = 'C';
    else if ((gr >= 61) && (gr <= 70))
          gr = 'P';
    else
        gr = 'F';
    return gr;
}

float calcAverage(nd head)
{
      nd temp;
      temp=head;
      int sum = 0, num;
      float avg;
     
     
      while ( temp->next != NULL )
      {
              sum+=temp->score;
        num+=1;
        avg = (float) sum / num;
        return avg;
       
      }
     
}

int search(nd head)
{
    int i,res = -1;
    nd temp;
    temp=malloc(sizeof(STUD));
    temp -> next = NULL;
    char id[5];
   
    FLUSH;
    printf("ID: ");   
    gets(temp -> sId);
    while(temp->next != NULL)
    {
          if (strcmp(temp->sId,temp->next->sId) == 0)
          {
                res = i;
                break;
          }
    }                   
    return res;
}

void inquireStudent(nd head)
{
   
    nd temp;
    char name[30],gr;
    float avg;
    temp=malloc(sizeof(STUD));
    temp -> next = NULL;
   
    while (temp != NULL && strcmp(temp->name, name) != 0)
    {
          temp = temp->next;
    }

    if (temp == NULL)
    {
        showError();
        return;
    }
    else
    {
          showName(head);
          showScore(head);
          avg = calcAverage(head);
          printf("\nAverage: %0.2f",avg);
          gr = getGrade(avg);
          printf("\nGrade: %c",gr);
          getch();
    }
    return;
}

void showAll(nd head)
{
    nd temp;
    temp=malloc(sizeof(STUD));
    temp -> next = NULL;
    if (head==NULL)
        printf ("No elements to print!\n");
    else {
        temp=head;
        do {
            system("cls");
              printf("Student List:\n\n");
              printf("Student ID\tStudent Name\n\n");
              printf("%s\t\t%s\n",temp -> sId, temp -> name);
            temp=temp->next;
        } while (temp!=NULL);
    }   
         
    getch();
    return;
}

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In most of your functions, you take a "head" pointer as a parameter to the function; then you allocate a node called temp, and set its next to NULL, and proceed to iterate through temp. Since you just allocated temp, the function will behave the same way no matter what head you pass in. For the functions that are simply examining the linked list, you probably want to set temp to point to head (instead of allocating a new node with malloc). And for the functions that are supposed to create a node, you need to add temp back into the head somehow. Whenever you call malloc(), you're grabbing new memory and leaving the existing head and existing list alone.

how do you recommend me pointing temp back into head?

Presumably something akin to "temp->next = head" or to "head->next = temp" will be relevant. There's more to it than that but that's something for you to work out. Don't rely on guess work. Reason it out.

There is also the less-than-incidental problem that your code wouldn't compile anyway. Since compilers tend to tell you what's wrong when they refuse to compile your code (albeit, in compiler-speak so some effort to interpret the messages will be needed), your first step needs to be understanding the error messages, and the second needs to be correcting the problems that cause them.