C Program A Simple Student Grades Database

#include <stdio.h> 
 #include <ctype.h> 
 #include <stdlib.h> 
 #define CLASSES 3 
 #define GRADES  5 
 int grade[CLASSES] [GRADES]; 
 void enter_grades(void); 
 int get_grade(int num); 
 void disp_grades(int g[][GRADES]); 
 int main(void) 
 { 
       char ch, str[80]; 
       clrscr(); 
       for(;;) { 
       do 
    { 
         printf("(E)nter Grades\n"); 
         printf("(R)eport Grades\n"); 
         printf("(Q)uit\n"); 
         gets(str); 
             ch = toupper(*str); 
    }  while(ch!='E' && ch!='R' && ch!='Q'); 
        switch(ch) 
              { 
                          case 'E': 
                                                 enter_grades(); 
                                                 break; 
                          case 'R': 
                                                 disp_grades(grade); 
                                                 break; 
                          case 'Q': 
                                                 exit (0); 
              } 
 } 
 } 
          /* Enter the student's grades. */ 
         void enter_grades(void) 
     { 
          int t, i; 
          for(t=0; t<CLASSES; t++) 
              { 
                  printf("Class # %d:\n", t+1); 
                  for(i=0; i<GRADES; ++i) 
                  grade[t][i] = get_grade(i); 
              } 
      } 
             /* Read a grade. */ 
             int get_grade(int num) 
         { 
                 char s[80]; 
                 printf("Enter Grade for Student # %d : ", num+1); 
                 gets(s); 
                 return(atoi(s)); 
         } 
                /* Display grades. */ 
             void disp_grades(int g[][GRADES]) 
         { 
              int t, i; 
              for(t=0; t<CLASSES; ++t) 
                  { 
                      printf("Class # %d:\n", t+1); 
                      for(i=0; i<GRADES; ++i) 
                      printf("Student #%d is %d\n", i+1, g[t][i]); 
                  } 
         }