Program in C to count number of vowels

Write a program in C to count number of vowels

#include <stdio.h>

void main ()

{

            char s[20],vw=0,i;

            clrscr();

            printf ("Enter any string: ");

            gets (s);

            for (i=0;i<=strlen(s);i++)

            {

                        switch (s[i])

                        {

                                    case 'a':

                                    case 'e':

                                    case 'i':

                                    case 'o':

                                    case 'u':

                                    case 'A':

                                    case 'E':

                                    case 'I':

                                    case 'O':

                                    case 'U':

                                    vw++;

                        }

            }

            printf ("There are %d vowels in it",vw);

            getch ();

}