Gradebook, array not saving - c

Question

So I'm trying to make a grade book that does everything displayMenu() says. But i cant even get the student ID to save when i go to view the grades. Please Help.
Everything is initialized here
#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <stdlib.h>
#define PAUSE system("pause")
#define CLS system("cls")
#define EXAMS 100
#define STUDENT 4
void displayArray(float grades[STUDENT][EXAMS]);
void newStudent(float grades[STUDENT][EXAMS]);
void displayStudentAverage(float grades[STUDENT][EXAMS]);
int main() {
float grades[STUDENT][EXAMS];
This is everything the program should do
displayMenu(grades, 0 );
} // end of main;
int displayMenu(float grades[STUDENT][EXAMS]) {
printf("\t \t MENU \t \t");
printf("Enter Corresponding Number\n");
printf("1.Enter New Student\n");
printf("2.Change Existing Grades\n");
printf("3.View All Grades\n");
printf("4.View Average Score Per Student\n");
printf("5.View Average Score Per Exam\n");
printf("6.View Average Score For The class\n");
printf("7.CLEAR GRADEBOOK\n");
printf("8. Save Gradebook\n");
printf("8.Exit\n");
int choice = 0;
scanf("%d", &choice);
switch (choice) {
case 1:
newStudent(grades, 0);
CLS;
displayMenu(grades,0);
break;
case 2:
break;
case 3: displayArray(grades, 0);
CLS;
displayMenu(grades,0);
break;
case 4:
displayStudentAverage(grades, 0);
break;
case 5:
break;
case 6:
break;
case 7:
break;
case 8:
exit(0);
break;
case 9:
exit(0);
break;
default: printf("You Have entered an incorrect number");
PAUSE;
}
}
This is what displays the grades
void displayArray(float grades[STUDENT][EXAMS]) {
printf("%.1f\t", grades[STUDENT][EXAMS]);
}
I'm trying to add the values to the array here
void newStudent(float grades[STUDENT][EXAMS]) {
float addgrade;
printf("Please Enter Student ID: ");
scanf("%f", &grades[STUDENT][EXAMS]);
printf("Enter four exam grades, use comma to split grades");
scanf("%f", addgrade);
grades[STUDENT][EXAMS] += addgrade;
PAUSE;
CLS;
}
void displayStudentAverage(float grades[STUDENT][EXAMS]) {
int sum, loop;
float avg;
sum = avg = 0;
for (loop = 0; loop < 10; loop++) {
sum = sum + grades[loop];
}
avg = (float)sum / loop;
printf("Average of array values is %.2f", avg);
}

Answer 1

First of all, it's always good check the compiler warnings to get some hints to possible bugs...
Here's a list of problems in the code:
no header files included
displayMenu prototype is missing
the grades array is used with inconsistent types (float/int)
with grades[STUDENT][EXAMS] the grades array is accessed out of bounds (for example if you define an array of size 5 you can only access position 0 to 4)
the return type of main needs to be int
the function newStudent has return type void but the code tries to return something with return &grades[STUDENT][EXAMS];
Apart from that, the code should work...