#include<iostream.h> // should be <iostream> without the .h
main() // should be int main()
{
int i, pass; // always give your vars a value: int i=0,pass=0;

cout<<"\n\t Enter a number:";
// this loop does nothing because i=1 and it loops until i is smaller then or equal to one, wich will happen on the first pas
for(i=1;i<=1;i++) 
{
cin>>pass;
} // you probably don't want this brace here. It ends your loop.
{ // <-- useless brace
if (pass==3)
{
cout<<"\n\t The password you entered is correct";
}
else
// From here on, everything is wrong. 
// You don't need to write the same code over and over again.
// That's what loops are for
{
cout<<"\n\t Enter a number:";
cin>>pass;
}
if (pass==3)
{
cout<<"\n\t The password you entered is correct";
}
else
{
cout<<"\n\t Enter a number:";
cin>>pass;
i++; // <--- don't do this. I is incremented by the for-loop
}
{// <-- useless brace
cout<<"\n\t Program Over!!!";
}// <-- useless brace
}// <-- useless brace
return 0;
}

#include <iostream>
 
using std::cin;
using std::cout;
 
int main(){
    for (int i = 0; i < 3; i++){ // loop 3 times
        int user_number = 0;
        cout << "Enter a number: ";
        cin >> user_number;
        cout << "Number " << i+1 << " entered was: " << user_number << '\n';
    }
}

#include <iostream.h>
 
int main(){
    for (int i = 0; i < 3; i++){ // loop 3 times
        int user_number = 0;
        cout << "Enter a number: ";
        cin >> user_number;
        cout << "Number " << i+1 << " entered was: " << user_number << '\n';
    }
}

#include<iostream.h>
int main()
{
int i=0, pass=0;
cout<<"Enter a number between 1 to 10:";
for(i=0; i<3; i++)
{
cin>>pass;
if (pass==3)
{
cout<<"The passcode you entered is correct!"; break;
}
else if (pass!=3)
cout<<"Enter a number between 1 to 10:";
else
cout<<"Program Over";  }
return 0;
}