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Some loops can be shown to always terminate or never terminate through human inspection. For example, the following loop will, in theory, never stop. However, it may halt when executed on a physical machine due to arithmetic overflow : either leading to an exception or causing the counter to wrap to a negative value and enabling the loop ...
Loop variants are used to guarantee that loops will terminate. A loop invariant is an assertion which must be true before the first loop iteration and remain true after each iteration. This implies that when a loop terminates correctly, both the exit condition and the loop invariant are satisfied.
try {// Try to read the file "file.txt" Scanner sc = new Scanner (new File ("file.txt")); while (sc. hasNextLine ()) System. out. println (sc. readLine ()); sc. close ...
The loop counter is used to decide when the loop should terminate and for the program flow to continue to the next instruction after the loop. A common identifier naming convention is for the loop counter to use the variable names i , j , and k (and so on if needed), where i would be the most outer loop, j the next inner loop, etc.
Do while loops check the condition after the block of code is executed. This control structure can be known as a post-test loop. This means the do-while loop is an exit-condition loop. However a while loop will test the condition before the code within the block is executed.
Infinite loops can be implemented using various control flow constructs. Most commonly, in unstructured programming this is jump back up , while in structured programming this is an indefinite loop (while loop) set to never end, either by omitting the condition or explicitly setting it to true, as while (true) ....
The halting problem is a decision problem about properties of computer programs on a fixed Turing-complete model of computation, i.e., all programs that can be written in some given programming language that is general enough to be equivalent to a Turing machine.
In C, break and continue allow one to terminate a loop or continue to the next iteration, without requiring an extra while or if statement. In some languages multi-level breaks are also possible. For handling exceptional situations, specialized exception handling constructs were added, such as try/catch/finally in Java.