Program in C to Calculate the Frequency of a Character in a given String

#include<stdio.h>
#include<string.h>
 
main()
{
   char a[100], ch;
   int c = 0, count[26] = {0};
 
   printf("Enter the String!\n");
   gets(a);
 
   while ( a[c] != '\0' )
   {
      if ( a[c] >= 'a' && a[c] <= 'z' ) 
         count[a[c]-'a']++;
      c++;
   }
 
   for ( c = 0 ; c < 26 ; c++ )
   {
      if( count[c] != 0 )
         printf("%c occurs %d times in the string!\n",c+'a',count[c]);
   }
   return 0;
}