ممكن مساعدة بحل السؤال رقم 6 بموعد اقصاه يوم الثلاثاء

انا حليت السؤال بس فيه ايرور وهذا الحل الخاص في
#include <iostream.h>
#include <fstream.h>
#include <string>
#include <cctype>
int main()
{
int i;
ifstream infile;
ofstream outfile;
char ans[21];
infile.open ("a:\\test.txt");
outfile.open ("a:\\grade.out");
cout<<"enter student's ID: "<<endl;
infile>>ans[21];
cout<<"enter student's answers: "<<endl;
for (i=1;i<=21;i++)
{
infile>>ans;
}
outfile<<"student's ID is: "<<ans[0];
outfile<<"the answer is: "<<endl;
for (i=1;i<=1;i++);
{
outfile<<ans;
}
char a[20]=('T','F','F','T','F','F','T','T','T','T','F','F','T','F','T','F','T','F','T');
int sum=0;
for (i=1;i<=20;i++);
{
if (ans{i}==a[i-1]);
sum=sum+2;
if ((ans0=!a[i-1])&&ans=!"F"&&ans=!"T"));
sum=sum+0;
else sum=sum-1;
}
cout<<"student score = "<<sum<<endl;
char grade;
if(sum>=90) grade='A';
if((sum>=80)&&(sum<=89.99)) grade='B';
if((sum>=70)&&(sum<=79.99)) grade='C';
if((sum>=60)&&(sum<=69.99)) grade='D';
else (sum>=50); grade='F';
cout<<"grade= "<<grade<<endl;
infile.close();
outfile.close();
return 0;
}