C - Counting Letters

#include <string.h>

int main()
{
    char s[1000];
    int  i, k, count=0, n, length;

    printf("Enter the string: ");
    gets(s);

    for(length=0;s[length];length++);
     n=length;

    for(i=0;i<n;i++)
    {
        count=1;
        if(s[i])
        {

          for(length=i+1;length<n;length++)
          {

            if(s[i]==s[length])
            {
                 count++;
                 s[length]='\0';
            }
          }
          printf("%c = %d \n",s[i],count);
       }
    }
    return 0;
}