Off-by-one error is an exceedingly common programming error.
For example, array access can easilly be off-by-one in languages whose compilers do not check array boundaries before compiling. An example of an off-by-one error causing out of bounds array access is shown in the following code:
dataArray[80];
for ( i=0; i <= 80; i++ )
dataArray[i] = 0;Because the array begins at 0 and not 1 (making the last array element 79, not 80), the for loop will cause the array to overflow. It is easy to see why this error is so common.