Arduino Uno : Unable to upload programs

Binary sketch size: 2970 bytes (of a 32256 byte maximum)
avrdude: verification error, first mismatch at byte 0x0000
0x0c != 0x00
avrdude: verification error; content mismatch

the board was working fine but this error cropped up ; i m unable to upload any programs

What did you do to cause the problem? What troubleshooting steps have you taken?

Posting to the forum is way down on the list of things to try. At the bottom, actually.

Post the OS you are using

ok so this was basically my 1st project building a line follower

i m using windows 7 / basic arduino package downloaded from the net

the last code that i have in the arduino

byte i=0;
boolean y=1;
unsigned int mival[4]={1023,1023,1023,1023};
unsigned int maval[4]={0,0,0,0},x=0;
void setup()
{
Serial.begin(9600);
}
void loop()
{
if(millis()<10000)
{
for(i=0;i<4;i++)
{
x=analogRead(i);
if(x>maval*)*
_ maval*=x;_
_ if(x<mival)
mival=x;
}
delay(20);
}
if(millis()>10000&&y==1)
{
Serial.write(“max :”);
for(i=0;i<4;i++)
Serial.println(maval);
Serial.write(“min :”);
for(i=0;i<4;i++)
Serial.println(mival);
y=0;
}*_

}
any tips on debugging measures are welcome

boolean y=1;

1?

The boolean type is chosen to indicate true or false. The initial value for y should be either true or false, not 1.

What do you have connected to analog pins 0 to 3?

Your line follower currently reads the values coming from 4 sensors, every 20 milliseconds, for 10 seconds, and keeps the largest and smallest value from each pin.

After 10 seconds, it prints the largest and smallest values from each pin.

After that, it does nothing. Hard to follow the line that way, but it IS good that you are developing in stages.

What changed between being able to upload, and not being able to?

yes that part was for sensor calibration ; essentially 4 sensors getting input ;

i m not able to upload any programs now

Paul could u plz suggest how i could debug the problem ; is it bootloader problem ?

Lots and lots of suggestions here: http://arduino.cc/en/Guide/Troubleshooting