HOJ 2892 YY, and YY again

http://acm.hit.edu.cn/hoj/problem/view?id=2892

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

int main()
{
int len, i, sum;
char str[256];

while(gets(str))
{
sum = 0;
len = strlen(str);
for (i = 0; i < len; i++)
{
if ( ! ( (str[i] >= 'A') && (str[i] <= 'Z') ) )
{
str[i] = 0;
}
else
{
str[i] = str[i] - 'A' + 1;
}
sum+=str[i];
}
if (sum > 100)
printf("INVALID\n");
else
printf("%d\n", sum);
}

return 0;
}