I've managed to write this following program which accepts values for 5 students and works on it. But, for the life of me, I can't figure out how to modify this for 'n' number of students! I've tried almost everything I know but I can't get it to work without errors! Does anyone have any ideas? Thanks!

Code :
#include <stdio.h> 
#include <conio.h>
#include <stdlib.h> 
 
#define NUM_STUDENTS 5 
 
#define IND_REGNO 0 
#define IND_FAIL 1 
#define IND_RANK 2 
#define IND_TOTAL 3 
#define IND_MARKS 4 
 
int st[NUM_STUDENTS][9]; 
int sortarr[NUM_STUDENTS]; 
 
int sortfunc(const void* p1, const void* p2) { 
    int id1=*(int*)p1, id2=*(int*)p2; 
 
    return st[id2][IND_TOTAL]-st[id1][IND_TOTAL]; 
} 
 
int main() { 
    printf("\n Enter the register number and marks in each subject");
    int i, j, passers=0, passrate=0, topper=0; 
 
    for(i=0; i<NUM_STUDENTS; i++) { 
        scanf("%i %i %i %i %i %i", &st[i][IND_REGNO], &st[i][IND_MARKS+0], &st[i][IND_MARKS+1], 
              &st[i][IND_MARKS+2], &st[i][IND_MARKS+3], &st[i][IND_MARKS+4]); 
 
        for(j=0; j<5; j++) { 
            st[i][IND_TOTAL]+=st[i][IND_MARKS+j]; 
            if(st[i][IND_MARKS+j] < 50) { 
                st[i][IND_FAIL]=1; 
            } 
        } 
 
        if(st[i][IND_FAIL] == 0) { 
            passers++; 
        } 
    } 
 
    for(i=0; i<NUM_STUDENTS; i++) { 
        sortarr[i]=i; 
    } 
 
    qsort(sortarr, NUM_STUDENTS, sizeof(int), sortfunc); 
 
    for(i=0; i<NUM_STUDENTS; i++) { 
        st[sortarr[i]][IND_RANK]=i+1; 
    } 
    passrate=(passers*100) / NUM_STUDENTS; 
    topper=st[sortarr[0]][IND_REGNO]; 
printf("\nNo \tM1 \tM2 \tM3 \tM4 \tM5 \tTOTAL \tP/F \tRANK \n \n \n");
    for(i=0; i<NUM_STUDENTS; i++) { 
        printf("\n%i \t%i \t%i \t%i \t%i \t%i \t%i \t%s \t%i\n", st[i][IND_REGNO], st[i][IND_MARKS+0], st[i][IND_MARKS+1], 
              st[i][IND_MARKS+2], st[i][IND_MARKS+3], st[i][IND_MARKS+4], st[i][IND_TOTAL], 
              (st[i][IND_FAIL]==0) ? "PASS" : "FAIL", st[i][IND_RANK]); 
    } 
 
    printf("\nPass Percentage - %i%%\nTopper - %i\n", passrate, topper); 
    getch();
    return 0; 
}