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uses crt;
const fi='vb.txt';
var f1:text;
st:string;
i,d:integer;
begin
clrscr;
assign(f1,fi); rewrite(f1);
readln(st);
d:=length(st);
for i:=1 to d do
if st[i] in ['A'..'Z'] then write(f1,st[i]:4);
close(f1);
readln;
end.

uses crt;
const fi='dulieu.dat';
var f1:text;
a,b,p,s:array[1..100]of real;
i,n:integer;
begin
clrscr;
assign(f1,fi); reset(f1);
n:=0;
while not eof(f1) do
begin
n:=n+1;
readln(a[n],b[n]);
end;
for i:=1 to n do
begin
p[i]:=(a[i]+b[i])/2;
s[i]:=a[i]*b[i];
end;
for i:=1 to n do
writeln(p[i]:4:2,' ',s[i]:4:2);
close(f1);
readln;
end.

Câu 1:
uses crt;
var st:string;
d,i,dem:integer;
begin
clrscr;
write('Nhap xau:'); readln(st);
d:=length(st);
write('Xau sau khi xoa so la: ');
for i:=1 to d do
if not(st[i] in ['0'..'9']) then write(st[i]);
writeln;
dem:=0;
for i:=1 to d do
if st[i]=#32 then inc(dem);
writeln('Xau co ',dem,' dau cach');
writeln('Do dai cua xau la: ',d);
readln;
end.
Câu 2:
uses crt;
const fi='kq.out';
var st1,st2:string;
f1:text;
begin
clrscr;
write('Nhap xau thu 1:'); readln(st1);
write('Nhap xau thu 2:'); readln(st2);
assign(f1,fi); rewrite(f1);
if length(st2)>length(st1) then writeln(f1,st2)
else writeln(f1,st1);
close(f1);
end.

const fi='vao.inp';
fo='ra.out';
var f1,f2:text;
st:string;
i,d:integer;
begin
assign(f1,fi); reset(f1);
assign(f2,fo); rewrite(f2);
readln(f1,st);
d:=length(st);
for i:=1 to d do
if st[i]='a' then delete(st,i,1);
writeln(f2,st);
close(f1);
close(f2);
end.

uses crt;
const fi='xau.txt';
var f1:text;
s:string;
i,d,kt:integer;
begin
clrscr;
assign(f1,fi); reset(f1);
readln(f1,s);
d:=length(s);
kt:=0;
for i:=1 to d do
if st[i]<>st[d-i+1] then kt:=1;
if kt=0 then writeln('Xau doi xung')
else writeln('Xau khong doi xung');
readln;
end.
uses crt;
const fi='vb.txt';
var f:text;
st:string;
begin
clrscr;
assign(f,fi); reset(f);
readln(f,st);
writeln('Xau co trong file la: ',st);
close(f);
readln;
end.