Resistive Touch Screens
I think the reading is taken from the other axis. So if you want to read the X axis you apply power/ground to the X wires and read the ADC connected to Y.
If you notice in the code snippet it says power is applied to X axis but reading is taken from CH0 (RA0) and named result_y (I think the diagram may have RC0 and RC3 connections mixed up though):

//Set PORTA To Inputs/High Impedance
TRISAbits.TRISA0 = 1;
TRISAbits.TRISA1 = 1;

//Set Lower 2 Bits to High Impedance
TRISCbits.TRISC0 = 1;
TRISCbits.TRISC1 = 1;
//Set Higher 2 Bits to Output
TRISCbits.TRISC2 = 0;
TRISCbits.TRISC3 = 0;

PORTCbits.RC0 = 0;
PORTCbits.RC1 = 0;
//Provide Ground To X-axis Of Touch Screen
PORTCbits.RC2 = 0;
//Provide Power To X-axis Of Touch Screen
PORTCbits.RC3 = 1;

// configure A/D convertor
OpenADC( ADC_FOSC_32 &amp; ADC_RIGHT_JUST &amp; 
ADC_8ANA_0REF,ADC_CH0 &amp; ADC_INT_OFF );

Delay10TCYx( 5 ); // Delay for 50TCY
ConvertADC(); // Start conversion
while( BusyADC() ); // Wait for completion
result_y = ReadADC(); // Read result
CloseADC();