I am new to programming and don't know what is wrong. I've tried to fix it for about a day now.
#include <iostream>
#include <string>

int main ()

{
using std::cout;
using std::cin;
using std::string;
string enter = "";
int gold;
int number;
int america;
int newgold;
int twogold, city, threegold;

cout << "Welcome to the coin game. "
<< "The objective is to get 1000 coins by the end.\n"
<< "(Press 1 and hit enter to continue.)\n";

cin >> enter;

cout << "\nFirst, solve 432 * 23, "
<< "in order to get your first 50 coins "
<< "(no calculators!).\n";
cin >> number;
if (number != 9936)
cout << "Sorry, you do not get 50 coins.";
else {
cout << "Congratulations, you now have 50 coins!";
gold = 0 + 50;

}
cout << " The next test is to figure out how old America is as of 2011.\n"
<< " (worth 75 coins.)\n";
cin >> america;

if ( america != 235 ) {
cout << "Sorry, you do not get 75 coins.\n"
<< "You have "
<< gold
<< " coins.";
}
else {
cout << "Congratulations, you now have "
<< (gold + 75)
<< " coins!\n";
newgold = gold + 75;
}
cout << "Now for your next question.\n"
<< "What is N.Y. City's approximate population?";
cin >> city;

if (city != 8000000)
twogold = newgold + 0;
cout << "Sorry, you do not get 75 coins.\n"
<< "You still have "
<< twogold
<< " coins.";

else { // Error: Expected '}' before 'else'.
cout << "Congratulations, you now have "
<< twogold = newgold + 75;
<< " coins.";
}
using std::cout;
using std::cin;
cout << "This next question is worth 200 coins!\n"
// Error: Expected constructor, destructor, or type conversion before '<<' token.
<< "How old would Martin Luther King Jr. "
<< "be as of January 1, 2011?";
cin >> king; // Error: Expected constructor, destructor, or type conversion before '>>' token.

if (king != 0 ) // Error: Expected unqualified-id before 'if'.
threegold = twogold + 0
cout << "Yikes! " // Error: Expected constructor, destructor, or type conversion before '<<' token.
<< "You do not get 200 coins.\n"
<< "You still have "
<< threegold
<< " coins."

else {
threegold = twogold + 200
cout << "Congratulations, you get 200 coins!"
<< "You now have "
<< threegold
<< " coins."
}


return 0; // Error: Expected unqualified-id before return.

} // Error: Expected declaration before '}' token.