Which US President was not born in the US?
George Washington, John Adams, Thomas Jefferson, James Madison, James Monroe, John Quincy Adams, Andrew Jackson, Martin Van Buren and William Henry Harrison were all born before the United States was created. However, they were all born in what is now the United States. John Tyler, the tenth president and born in 1790, was the first president "born in the USA."
What if parents of a us president was not born in the us and are not citizens but the president was born in the us?
No. Any person running for president must have been born in the USA. You are correct that a foreigner cannot be president, because you must be a US citizen by birth. However, your answer contains a common misconception. You do not have to be born in the US to be president, which is called native-born, but must be natural-born, which means either born on US soil or to a US citizen.
President Obama was born in Hawaii. Neither Hawaii nor Alaska are part of the "continental US." The first nine US Presidents were born on British soil because they were born within the thirteen colonies before they won their independence. John Tyler, the tenth president, was the first president "born in the USA."
A natural-born US citizen of Mexican descent can be elected President, but a person born in Mexico cannot. Article II, Section 1, Paragraph 5 of the Constitution specifies the President (and Vice-President) must be natural-born, meaning born in one of the US States, US Territories, or on a US military base. Naturalized US citizens are not eligible to run for President.