s = input("Nhập một xâu bất kỳ: ")

print("Các ký tự và chữ số trong xâu là:")

for char in s:

       if char.isdigit() or char.isalpha():

              print(char)

Cho mình hỏi isalpha là gì vậy ạ ?

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.

Use crt;

Var S : String;

P: longint;

Begin

Write('Nhap s: '); readln (S);

For P:=length(S) downto 1 do

Write(P);

Readln;

End.

uses crt;

var st:string;

i,d:integer;

begin

clrscr;

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

d:=length(st);

writeln('Xau ban vua nhap la: ',st);

writeln('Xau nguoc la: ');

for i:=d downto 1 do

write(st[i]:4);

readln;

end.

Program HOC24;

var s: string;

begin

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

write('Xau sau khi loc: ');

for i:=1 to length(s) do

if s[i] in ['A'..'z'] then write(s[i]);

readln

end.

uses crt;

var st:string;

a:array[1..255]of string;

i,d,dem,kt,j,dem1:integer;

begin

clrscr;

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

d:=length(st);

a[1]:=st[1];

dem:=1;

for i:=1 to d do 

  begin

kt:=0;

for j:=1 to dem do 

  if st[i]=a[j] then kt:=1;

if kt=0 then 

begin

inc(dem);

a[dem]:=st[i];

end;

end;

for i:=1 to dem do 

  begin

dem1:=0;

for j:=1 to d do 

  if a[i]=st[j] then inc(dem1);

writeln(a[i],' xuat hien ',dem1,' lan');

end;

readln;

end.

uses crt;

var a:string;

     c:char;

     i,dem:integer;

begin

    clrscr;

    readln(a);

    readln(c);

    dem:=0;

    for i:=1 to length(a) do

    if a[i]=c then dem:=dem+1;

    writeln(dem);

    readln;

end.

cau 1:

uses crt;

var a:array[1..100] of integer;

n,i,min: integer;

begin

readln(n);

for i:=1 to n do

readln(a[i]);

min:=a[1];

for i:=2 to n do

if min>a[i] then min=a[i];

writeln(a[i]);

readln;

end.

cau 2:

uses crt;

g:text;

s:string;

const fo='CHUSO.TXT';

begin

assign(g,fo);

rewrite(g);

readln(s);

for i:=1 to length(s) do

if not((s[i] in ['a'..'z'])and(s[i] in ['A'..'Z])) then delete(s,i,1);

writeln(g,s);

end.

Program Xau;

Uses crt;

Var St: String;

    i: longint;

Begin

        Clrscr;

        Write('Nhap xau: '); Readln(St);

        For i:=1 to length(St) do

                St[i] := Upcase(St[i]);

        Write('St = ',St);

        Readln

End.

2:

uses crt;

var st:string;

d,i,dem1,dem2:integer;

begin

clrscr;

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

d:=length(st);

dem1:=0;

dem2:=0;

for i:=1 to d do

  begin

if st[i] in ['0'..'9'] then inc(dem1);

if (st[i] in ['a'..'z']) or (st[i] in ['A'..'Z']) then inc(dem2);

end;

writeln('So ki tu la chu so la: ',dem1);

writeln('So ki tu la chu cai la: ',dem2);

for i:=1 to d do 

  if st[i] in ['0'..'9'] then delete(st,i,1);

writeln('Xau sau khi xoa cac chu so la: ',st);

readln;

end.