Facing problem while initializing an array

Question

I am facing a problem while initializing an array in C. I am trying to take input of a variable 'n' and declare an array marks[n] with its value set to zero. I wrote the following part of the program to do it.

int n,k,e,m,x;
scanf("%d %d %d %d", &n,&k,&e,&m);
int marks[n]={0};

but executing the program generates the following warnings and errors:

prog.c: In function ‘main’:

prog.c:10:6: error: variable-sized object may not be initialized
      int marks[n]={0};
      ^~~

prog.c:10:20: warning: excess elements in array initializer
      int marks[n]={0};
                    ^

prog.c:10:20: note: (near initialization for ‘marks’)

This is the whole program:

    #include <stdio.h>
int main(int argc, char const *argv[])
{
int t;
scanf("%d",&t);
for (int z = 0; z < t; ++z)
{
    int num_candidate,num_seat,num_exam,max_mark,mark_needed;
    scanf("%d %d %d %d", &num_candidate,&num_seat,&num_exam,&max_mark);
    int marks[num_candidate]={0};
  /*gets the total marks of each students. mark of the last exam of the */
  /*num_candidate-th student is not taken */
    for (int i = 0; i < num_candidate; ++i)
    {
        for(int j=0;j<num_exam;j++)
        {
            if (i==num_candidate-1 && j==num_exam-1)
            {
                break;
            }
            scanf("%d",&mark_needed);
            marks[i]=marks[i]+mark_needed;
        }
    }
             /*sorting*/
    for (int i = 0; i < num_candidat-2; i++)
    {
        for(int j=i; j<num_candidat-2; j++)
        {
            if (marks[j]<marks[j+1])
            {
                int temp = marks[j];
                marks[j]= marks[j+1];
                marks[j+1]=temp;
            }
        }
    }
        /*prints the needed marks*/
    mark_needed=marks[num_seat-1]-marks[num_candidat-1];
    printf("%d\n",mark_needed+1 );
}


return 0;
}

My goal is to take num_candidate=number of candidates, num_seat= number of seats in the school, num_exam=number of exams, max_mark=maximum achievable marks in a single exam. I want to know how many marks the n-th student would need in his final exam to be admitted. his mark of the last exam is not taken as an input in the program and I want to figure out the least marks he would need in the final exam.

How can I solve it?

Answer 1

From the C Standard (6.7.9 Initialization)

3 The type of the entity to be initialized shall be an array of unknown size or a complete object type that is not a variable length array type.

So instead of this declaration with an initializer

int marks[n]={0};

use

int marks[n];
memset( marks, 0, n * sizeof( int ) );

Pay attention to that n may not be equal to zero.