hdu 2399 GPA

http://acm.hdu.edu.cn/showproblem.php?pid=2399

#include<stdio.h>
#include<string.h>
int main()
{
char s[1000];
while(gets(s))
{
 double j=0.00;

int sum=0,tag=1;
for(int i=0;i<strlen(s);i++)
{
if(s[i]==' ')

continue;
if(s[i]=='A')

{

sum+=4;

j++;

}
else if(s[i]=='B')

{

sum+=3;

j++;

}
else if(s[i]=='C')

{

sum+=2;

j++;

}
else if(s[i]=='D')

{

sum+=1;

j++;

}
else if(s[i]=='F')

{

j++;

}
else {
 printf("Unknown letter grade in input\n");
 tag=0;
 break;
 }
}
if(tag==1)
printf("%.2f\n",sum/j);
}
return 0;
}