Bài 3: 

uses crt;

const fi='teptong.txt';

var a,b:integer;

f1:text;

begin

clrscr;

assign(f1,fi); rewrite(f1);

readln(a,b);

writeln(a+b);

writeln(f1,a+b);

close(f1);

readln;

end.

uses crt;

var a,b:string;

i,d:integer;

begin

clrscr;

write('Nhap xau a:'); readln(a);

d:=length(a);

b:='';

for i:=1 to d do 

  if a[i] in ['A'..'Z'] then b:=b+a[i];

writeln(b);

readln;

end.

Bài 1:

uses crt;

var S:String;

vt:integer;

begin

clrscr;

Write(‘Nhap 1 xau:’); Readln(S);

While pos(‘nang’,s)>0 do

Begin

Vt:= pos(‘nang’,s);

Delete(s,vt,4);

Insert(‘mua’,s ,vt);

End;

Writeln(‘Xau sau khi thay the ’,s);

Readln;

End.

Bài 2: 

uses crt;

var st:string;

d,i,kt:integer;

begin

clrscr;

write('Nhap xau:'); readln(st);

d:=length(st);

kt:=0;

for i:=1 to d do 

  if st[i]<>st[d-i+1] then kt:=1;

if kt=0 then writeln(st,' la xau doi xung')

else writeln(st,' khong la xau doi xung');

readln;

end.

uses crt;

var s:string;

i,d,dem:integer;

begin

clrscr;

write('Nhap xau S:'); readln(s);

d:=length(s);

writeln('Cac ki tu so co trong xau S:'); 

dem:=0;

for i:=1 to d do 

  if s[i] in ['0'..'9'] then

begin

write(s[i]:4);

inc(dem);

end;

writeln;

writeln('So ki tu chu so co trong xau S: ',dem);

for i:=1 to d do 

  if s[i] in ['0'..'9'] then s[i]:='A';

writeln('Xau sau khi doi la: ',s);

readln;

end.

Program HOC24;

var i,d1,d2: byte;

st1,st2: string[60];

begin

write('Nhap xau st1: '); readln(st1);

//---------------Câu 1-------------------

d1:=0; d2:=0;

for i:=1 to length(st1) do

begin

if st1[i]='A' then d1:=d1+1;

if st1[i]='a' then d2:=d2+1;

end;

writeln('Co ',d1,' ki tu A trong xau');

writeln('Co ',d2,' ki tu a trong xau');

//---------------------- Câu 2 --------------------

st2:='';

for i:=1 to length(st1) do if st1[i] in ['a'..'z'] then st2:=st2+st1[i];

writeln('Xau st2 la: ',st2);

//------------------------------Câu 3--------------------

for i:=1 to length(st1) do st1[i]:=upcase(st1[i]);

write('Xau st1 sau khi in hoa la: ',st1);

//--------------------------------------------------------

readln

end.

Chỗ câu 1 câu 2 câu 3 là s vậy ạ

program stringManipulation;

var
  st1, st2: string;
  countN, i: integer;

begin
  write('Nhap vao xau ki tu st1: ');
  readln(st1);
  countN := 0;
  for i := 1 to length(st1) do
  begin
    if (st1[i] = 'N') or (st1[i] = 'n') then
    begin
      countN := countN + 1;
    end;
  end;
  writeln('So ky tu N va n trong xau st1 la: ', countN);
  st2 := '';
  for i := 1 to length(st1) do
  begin
    if (st1[i] >= 'A') and (st1[i] <= 'Z') then
    begin
      st2 := st2 + st1[i];
    end;
  end;
  writeln('Cac ky tu in hoa trong xau st1 la: ', st2);
  write('Xau st1 viet theo chieu nguoc lai la: ');
  for i := length(st1) downto 1 do
  begin
    write(st1[i]);
  end;
  readln;
end.

st1 = input("Nhập vào xâu kí tự: ")
count_n = 0
st2 = ""
for char in st1:
    if char == 'N' or char == 'n':
        count_n += 1
    if char.isupper():
        st2 += char

print("Số lần xuất hiện của kí tự 'N' và 'n' là:", count_n)
print("Xâu kí tự chỉ chứa kí tự in hoa là:", st2)
print("Xâu kí tự đảo ngược là:", st1[::-1])

uses crt;

var st:string;

d,i:integer;

begin

clrscr;

readln(st);

d:=length(st);

for i:=1 to d do 

  if not (st[i] in ['0'..'9']) then write(st[i]);

readln;

end.