C-Program to count vowels in sentence

#include<stdio.h>

#include<string.h>

int main()

{

    int i,vowelcount=0;

    char str[100];

    printf("Enter a string\n");

    gets(str);

    for(i=0;i<strlen(str);i++)

    {

        if(str[i]=='A'||str[i]=='a'||str[i]=='e'||str[i]=='E'||str[i]=='I'

        ||str[i]=='i'||str[i]=='O'||str[i]=='o'||str[i]=='U'||str[i]=='u')

        {

            vowelcount++;

        }

    }

    printf("%d\n",vowelcount);

    return 0;

}