Collision questions

I need some help with precise collision in my game. I already got code working, but somehow it glitches up when I land on the ground. First, here is the collision code:

bool check_collision( std::vector<SDL_Rect> &A, std::vector<SDL_Rect> &B )
{
	//The sides of the rectangles
	int leftA, leftB;
	int rightA, rightB;
	int topA, topB;
	int bottomA, bottomB;

	//Go through the A boxes
	for( int Abox = 0; Abox < A.size(); Abox++ )
	{
		//Calculate the sides of rect A
		leftA = A[ Abox ].x;
		rightA = A[ Abox ].x + A[ Abox ].w;
		topA = A[ Abox ].y;
		bottomA = A[ Abox ].y + A[ Abox ].h;

		//Go through the B boxes
		for( int Bbox = 0; Bbox < B.size(); Bbox++ )
		{
			//Calculate the sides of rect B
			leftB = B[ Bbox ].x;
			rightB = B[ Bbox ].x + B[ Bbox ].w;
			topB = B[ Bbox ].y;
			bottomB = B[ Bbox ].y + B[ Bbox ].h;

			//If no sides from A are outside of B
			if( ( ( bottomA <= topB ) || ( topA >= bottomB ) || ( rightA <= leftB ) || ( leftA >= rightB ) ) == false )
			{
				//cout << "Touching" << endl;
				//A collision is detected
				return true;
			}
		}
	}
	//If neither set of collision boxes touched
	return false;
}

Here is the movement code of my player:

void player::move( std::vector<SDL_Rect> &rects )
{
	//Move the player left or right
	x += xVel;

	//Move the collision boxes
	shift_boxes();

	//If the player went too far to the left or right or has collided
	if( check_collision( box, rects ) )
	{
		//Move back
		x -= xVel;
		shift_boxes();
	}

	yNew = y + yVel;

	while ( y != yNew && yVel != 0 )
	{
		if (yVel >= 0)
		{
			y ++;
			cout << "y++;" << endl;
		} else {
			y --;
			cout << "y--;" << endl;
		}
		shift_boxes();
		// Check collisions at pixel level
		if( check_collision( box, rects ) )
		{
			if( falling == true && ( on_ground && jumping ) == false )
			{
				cout << "collision with ground" << endl;
				on_ground = true;
				falling = false;
			}
			if( jumping == true && ( on_ground && falling ) == false )
			{
				cout << "collision with ceiling" << endl;
				yVel = 0;
				air_time = air_climax;
			}
			if( on_ground == true && ( jumping && falling ) == false )
			{
				cout << "still on the ground" << endl;
				y -= yVel;
			}
			shift_boxes();
		} else {
			if ( jumping == false )
			{
				cout << "nothing below you so falling" << endl;
				falling = true;
				on_ground = false;
			}
		}
	}
}

Here is the air code of my player (which decides when to fall, after jumping):

void player::air()
{
	if( jumping == true && ( on_ground && falling ) == false )
	{
		//if( yVel > 0 ){ yVel = 0; }
		//if( yVel > -yspeed ){ yVel--; }
		yVel = -yspeed;
		if( air_time < air_climax )
		{
			air_time++;
		} else { //when air_time is greater than or equal to air_climax
			yVel = 0;
			falling = true;
			jumping = false;
		}
	}

	if( jumping == false ){ air_time = 0; }

	if( falling == true && ( on_ground && jumping ) == false )
	{
		//if( yVel < yspeed ){ yVel++; }
		yVel = yspeed;
	}
}

You will see I have commented out code in the player::air code, that is because I want to make this easier for you and for me right now. With my current code in player::movement, the part with the yNew variable and all that, I see that it collides spot on with the cieling (in some older code I had, which had y+=yVel instead of yNew = y + yVel and didn't have the "while ( y != yNew && yVel != 0 )" as well as the "if (yVel >= 0)" code in it, the player jumped at a contant rate and his head would stick into the cieling a little bit before the falling occured) and then falls. While it is jumping, it will print the "y--;" message to console, while it is falling it will do "y++;". When you are falling and land on the ground, the game freezes and prints about 6 or 7 "y++;" at an alarming rate to every "collision with ground" and once in awhile "nothing below you so falling" pops up.

I have no idea what needs to be fixed, but that is where the code I need help with is. If you think you need anything else to help me, just ask. Thanks