According to article i of the constitution, who has the power to declare war? what power does the constitution give the president in the area of war?

To answer your first question, Article 1, Section 8. This power is not shared with anyone, including the President. The President, however, is just as clearly made the Commander inChief of all of the armed forces. To answer your second question Under Article I, Section 8 of the U.S. Constitution, Congress has sole power "to declare war [and] grant letters of marque and reprisal." But Article II, Section 2 provides that "The president shall be Commander-in-Chief of the Army and Navy of the United States."