Generating a magic square

Question

This is a magic square problem, the size of the magic square n should be inputed as a command line argument. n has to be a odd number. The expected output should be like this. My problem is that when I try to execute the code, it generates a bunch of 0s.

I am a C beginner and I hope someone can help me with my problem. Thank you very much! I appreciate your help!

#include <stdio.h>
#include <stdlib.h>

int main(int argc, char *argv[])
{
    int n = atoi(argv[1]);
    int magic[n+1][n+1];
     if(argc == 2) 
        {
         for(int i = 0; i < n; i++) 
         {
            for(int j = 0; j < n; j++) 
            {
              magic[i][j] = 0;
            }
          }

          int i =0 ;//row
          int j= n / 2; //column

          for ( int k = 1; k <= n*n; k++ )
          {
             magic[j][i] = k;

             if(magic[j][i] == 0) //if the spot is empty
             {
                 if (j == 0 && i == 0)
                 {
                     j--;//go up one level
                     i--; //go left
                 }

                 else
                 {
                     if(j == 0) //if it's on the first row
                        j = n - 1;
                     else
                        j--;

                     if (i == 0) //if it's on the left column
                         i = n - 1;
                     else
                         i--;
                  }
              }

              else //if the spot is not empty
              {
                  j = j + 2;
                  i++;
              }
      }
  }


    for(int x=0; x<n; x++)
          {
             for(int y=0; y<n; y++)
                 printf("%3d", magic[x][y]);
             printf("\n");
          }

          return 0;
    }

Answer 1

You cannot use variables to declare the size of an array

 int magic[n+1][n+1];

You can:

1) Look up how to dynamically allocate arrays, or

2) Use a vector

Also, I don't think this is causing a problem now but

int n = atoi(argv[1]);

does not check to make sure that argv[1] contains numerical characters which may cause problems for you later.