char counting

#include<stdio.h>
#include<string.h>
#include<ctype.h>

int main()
{
    char a[1001];
    gets(a);
    int cnt[2001];
    memset(cnt,0,sizeof(cnt));
    int l=strlen(a),i;
    for(i=0; i<l; i++)
        cnt[(int)a[i]]++;
    puts("--by lexicographic order--");
    // by lexicographic order
    for(i=0; i<2001; i++)
    {
        if(cnt[i] && isalpha(i))
        {
            printf("%c had repeated for %d times\n",i,cnt[i]);
        }
    }
    puts("--by string order--");
    //by string order
    for(i=0; i<l; i++)
    {
        if(isalpha(a[i]) && cnt[(int)a[i]])
        {
            printf("%c has repeated for %d times\n",a[i],cnt[(int)a[i]]);
            cnt[(int)a[i]]=0;
        }
    }
    return 0;
}