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Sec. 12.3 in .NET Encode PDF417 in .NET Sec. 12.3

Sec. 12.3 use .net pdf-417 2d barcode integration tocreate barcode pdf417 for .net upc barcode An Undecidable Problem expected to take a ver y long time, there comes an agonizing moment when we have to give up hope that it is on the verge of producing a useful answer and stop the program on the assumption that it has entered an infinite loop. While it would be very nice to have a utility that would look over a program and predict how long it would run, most of us would settle for a device that would simply predict whether or not it will ever halt. It"s a good bet that you have never used such a device, which may at first seem strange since a solution to the halting problem would certainly provide information that would often be useful.

If you have never thought about this before, you might surmise that the scarcity of such programs is a consequence of anyone of several limiting factors. Perhaps they are inordinately expensive to run, or no one has taken the time to implement an existing scheme, or perhaps no one has yet figured out how to develop the appropriate algorithms. In actuality, no one is even looking for a "halting" algorithm, since no such algorithm can possibly exist.

Let us consider the implications that would arise if such an algorithm could be programmed in, say, Pascal. We can consider such an algorithm to be implemented as a Boolean function called HALT, which looks at whatever program happens to be in the file named data.p and returns the value TRUE if that program will halt, and returns FALSE if the program in data.

p would never halt. Perhaps this function is general enough to look at source code for many different languages, but we will see that it is impossible for it to simply respond correctly even when looking solely at Pascal programs. The programmer of the function HALT would likely have envisioned it to be used in a program such as CHECK, shown in Figure 12.

5. We will use it in a slightly different way and show that a contradiction arises if HALT really did solve the halting problem. Our specific assumptions are that:.

1. HALT is written in VS .NET PDF417 Pascal.

2. HALT always gives a correct answer to the halting problem, which means: a. It always returns an answer after a finite amount of time.

b. The answer returned is FALSE if the Pascal program in data.p would never halt.

c. The answer returned is TRUE if the Pascal program in data.p would halt (or if the program in data.

p will not compile).. Consider the program T EST in Figure 12.6, which is structured so that it will run forever if the function HALT indicates that the program in the file data. p would halt, and simply quits if HALT indicates that the program in data.

p would not halt. Some interesting things happen if we run this program after putting a copy of the source code for TEST in data.p.

If HALT does not produce an answer, then HALT certainly does not behave as advertised, and we have an immediate contradiction. HALT is supposed to be an algorithm, so it must eventually return with an answer. Since HALT is a Boolean function, we have only two cases to consider.

. program CHECK; { envis Visual Studio .NET PDF417 ioned usage of HALT function HALT: boolean; begin { marvelous code goes here end { HALT }. Decidability Chap. 12 begin { CHECK} if HALT then wri teln ( "The program in file data. p will halt" ) else writeln( "The program in file data.p will not halt") end { CHECK }.

. Figure 12.5 A possible usage of HALT Case 1: HALT returns a value of TRUE to the calling program TEST. This has two consequences, the first of which is implied by the asserted behavior of HALT..

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