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?

`int marks[n]` is a *VLA*. You cannot initialize VLAs. Try `int *marks = calloc(n * sizeof *marks);` -- then use `marks` as if it was an array and don't forget to `#include ` and `free()` the resources when you no longer need them. — pmg, Aug 02 '20 at 20:11
The error message is self-explanatory — you can't provide an initializer for a VLA (variable-length) array. — Jonathan Leffler, Aug 02 '20 at 20:11
Can you explain better the problem? I dont understand the goal of this question, if the problem is just the inizialiting of the array you have just to use the malloc, but if you want someone to solve the entire problem I didnt understand very well the question — KKKKK, Aug 02 '20 at 20:36
@pmg int marks[n]; *marks = calloc(n , sizeof (int)); i think this is what you meant. — Miraz, Aug 02 '20 at 20:39
@KKKKK I wanted to know the cause and solution of the stated problem. I have already solved the entire problem as you can see. Edit: Thanks for the solution. — Miraz, Aug 02 '20 at 20:42
dont forget to do `free(marks)` before the `return 0`, for memory leaks error — KKKKK, Aug 02 '20 at 20:43
@KKKKK Everything has already been said by pmg in the first comment. Don't misdirect Miraz by suggesting to use `malloc()` since `malloc()` doesn't do any initialization. Miraz: use `calloc()` as suggested by pmg. — xhienne, Aug 02 '20 at 20:47
Just a style comment -- I'm puzzled by your use of variable names. I thought we all outgrew single-character nonsensical variable names when we graduated from ROM-BASIC in 1978. In 2020, if you have to tell us what your variable names represent, you're doing it wrong. — TomServo, Aug 02 '20 at 22:18

Vlad from Moscow · Accepted Answer · 2020-08-02T22:19:41.133

3

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.

edited Aug 02 '20 at 22:19

answered Aug 02 '20 at 22:13

Vlad from Moscow

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Facing problem while initializing an array

1 Answers1