ON SIZE ERROR OPTION:

Whenever a size error occurs, the contents of the result field after the operation is unpredictable.  Though, the processing is not-terminated and the computer will continue with the execution of the next statement regardless of the fact that a size error occurred.

And hence, it is the responsibility of the programmer to monitor the arithmetic operation by identifying the ON SIZE ERROR phrase at the end of the arithmetic statement. It has the syntax which is as shown below:

ON SIZE ERROR   imperative - statement

Whenever this phrase is specified, then the imperative statement gets executed, if an ON SIZE ERROR occurs. However a statement

ADD  A  TO  B   ON  SIZE   ERROR    GO   TO   ERROR-PARA.

will cause the control to be transferred to the ERROR-PARA in the situation of the size error.

Or Else, the effect will be similar as that of the ADD A TO B.  Whenever the ON SIZE ERROR phrase is specified, the arithmetic statement should be terminated by the period.

The ON SIZE ERROR phrase allows a programmer to take the measures in case a size-error condition arises. Though, specifying the ON SIZE ERROR phrase with each and every arithmetic operation can increase the execution time of the program.Though when the programmer is sure that there is no possibility of the size error, the phrase may not be specified.

In this connection it is suggested that the programmer must give the result fields enough room, therefore the size error does not occur.

It may be valuable to note the differences between the ROUNDED and SIZE ERROR. The ROUNDED option is concerned with the situation when a loss of digits occurs at the right end side. This loss just makes the result estimated, but the result is not altogether wrong. The ROUNDED option affects only the nature of the approximation.  If specified, then the result is approximately by rounding. Or else, it is approximated be truncation. On the other hand, the SIZE ERROR is concerned with the case when a loss of digits occurs in the most significant part (left end side). The outcome in such a case is totally wrong.