line tracking.. off the line .. sensor programming issues

[canatan]

we're making a line tracking robot that runs off the line but along it...
so there was one sensor protruding from the front left corner..
and then our seniors asked us to put one in the back left corner and one in the middle next to the wheels for detecting junctions..
anyhoo each sensor set has 4 sensors 2 that are are on the corners of the line and 2 right outside .. all 4 sensors are in a str horizontal line..
what i dont get is how do i use the sensor in the middle for turning??

[SmAsH]

well, if you ae turning it will try to keep the center of the robot over the line so it doesn't stray away.

[canatan]

so i can combine the front and back sensors into one int and check with the middle ones?

[SmAsH]

make the robot turn the direction of the line but make sure the middle keeps reading that the line is there.