26:

uses crt;
var n,i:integer;
s1,s2:string;
begin
clrscr;
write('Nhap n:'); readln(n);
s2:='';
str(n,s1);
for i:=length(s1) downto 1 do
 s2:=s2+s1[i];
write('so ',n,' sau khi dao nguoc la:',s2);
readln
end.

27:

uses crt;
var n,i:integer;
s1,s2:string;
begin
clrscr;
write('Nhap n:'); readln(n);
s2:='';
str(n,s1);
for i:=length(s1) downto 1 do
 s2:=s2+s1[i];
if s1=s2 then write('n la so doi xung')
 else write('n ko phai la so doi xung');
readln
end.

28:

uses crt;
var n,i,a,code,max:integer;
s1,s2:string;
begin
clrscr;
write('Nhap n:'); readln(n);
s2:='';
str(n,s1);
max:=0;
for i:=1 to length(s1) do
begin
 val(s1[i],a,code);
 if max < a then max:=a;
end;
write('so lon nhat cua n la:',max);
readln
end.

29:

uses crt;
var n,i,a,code,min:integer;
s1,s2:string;
begin
clrscr;
write('Nhap n:'); readln(n);
s2:='';
str(n,s1);
min:=9;
for i:=2 to length(s1) do
begin
 val(s1[i],a,code);
 if min > a then min:=a;
end;
write('so nho nhat cua n la:',min);
readln
end.

26.

#include <bits/stdc++.h>
using namespace std;
string n;
int main() {
    cin >> n;
    for (long i=n.size(); i>=0; i--) cout << n[i];
}

27.

#include <bits/stdc++.h>
using namespace std;
int n,p,s,i;
int main() {
    cin >> n;
    for (i=n; n!=0; n/=10) {
        p=n%10;
        s=s*10+p;
    }
    if (i=s) cout << i << " la so doi xung";
    else cout << i << " khong la so doi xung";
}

28.

#include <bits/stdc++.h>
using namespace std;
int n,i,m;
int main() {
    cin >> n;
    m=n%10;
    while (n!=0) {
        i=n%10;
        if (m<i) m=i;
        n/=10;
    }
    cout << m;
}

29.

#include <bits/stdc++.h>
using namespace std;
int n,i,m;
int main() {
    cin >> n;
    m=n%10;
    while (n!=0) {
        i=n%10;
        if (m>i) m=i;
        n/=10;
    }
    cout << m;
}