Pointer conversion array capitalization

Using the offset address of the array element in uppercase to lowercase conversion, calculate the number to be converted and printed character array in the forward and rearward

#include<stdio.h>
#define n 20
main()
{
 char *a=NULL;
 unsigned int change_sum=0;
 unsigned int loop=0;
 char array[n]={'a','B','N','8','M','D',',','*','0','X','m','4','y','Z','!','t','U','T','k','@'};
 a=array;
 for(loop =0;loop<n;loop++)
 {
  if((loop%5)==0)
  {
   printf("\n");
  }
  printf("%-4c",*a++);
 } 
 printf("\n*********************\n\n");
 a=array;
 for(loop =0;loop<n;loop++)
 {
  if(('A'<=*a)&&(*a<='Z'))
  {
   *(array+loop)=*a+'a'-'A';
   change_sum++;
  }
  if((loop%5)==0)
  {
   printf("\n");
  }
  printf("%-4c",*a);
  a++;
 }
 printf("\nchange_sum=%u\n",change_sum); 
}