bài 2

#include<bits/stdc++.h>
using namespace std;
int main()
{
 double n;
 cin>>n;
 if (n==(int)n) {
  int z=n;
  if (z%2==0)
  cout<<z<<" la so chan";
  else cout<<z<<" la so le";
 }
 else cout<<floor(n);
}

bài 3

#include<bits/stdc++.h>
using namespace std;
int main()
{
 long long n;
 cin>>n;
 if (n%2==0)
 {
  for (int i=0;i<=n;i+=2)
  cout<<i<<" ";
 }
 else {
  for (int i=1;i<=n;i+=2)
  cout<<i<<" ";
 }
}

Bài 2: (mình chưa hiểu lắm)

Bài 3:

#include<bits/stdc++.h>
using namespace std;
int main()
{
    long n;
    printf("\nNhap n: "); cin>>n;
    if (n%2==0)
 {
    printf("\ncac so chan tu 1 den n: ");
    for (int i=0;i<=n;i+=2)
    cout<<i<<" ";
 }
 else {
    printf("\ncac so le tu 1 den n: ");
    for (int i=1;i<=n;i+=2)
    cout<<i<<" ";
 }
}