Count number of vowels for a given sentence(both lowercase and uppercase letters)

Given a sentence of words, count the number of vowels for the sentence which may contain both lowercase and uppercase alphabets.

#include <stdio.h>
#include<string.h>
#include<stdlib.h>
int main(void) {
   char *s;
   int vowels=0,consonants=0;
   s=(char*)malloc(sizeof(char));
   gets(s);
   while(*s)
   {
     if(*s>='A' && *s<='Z')
     {
      if(*s=='A' || *s=='E' || *s=='I' || *s=='O' || *s=='U')
       vowels++;
      else
       consonants++;
     }
     else if(*s>='a' && *s<='z')
     {
      if(*s=='a' || *s=='e' || *s=='i' || *s=='o' || *s=='u')
       vowels++;
      else
       consonants++;
     }
     s++;
   }
   printf("vowels = %d\n",vowels);
   printf("consonants = %d",consonants);
   return 0;
}