Connect and share knowledge within a single location that is structured and easy to search. C++ compilers need to do some amount of static analysis to determine whether any given loop could fit the requirements for the kind of transformation Pascal loops qualify for unconditionally. My full software code is C++, my 'i' is unsigned resgister int, Thus, youll want to print something like the following table of numbers, where the prices per unit are listed in the top row, and the prices for 2, 3 and 4 units are listed in subsequent rows: To produce this multiplication table, we could use the following nested for loops: Note how indenting is used here to distinguish the levels of nesting and to make the code more readable. Can somebody be charged for having another person physically assault someone for them? Can somebody be charged for having another person physically assault someone for them? let count = 0 while (count < 5) { basic.showNumber(count) count += 1 basic.pause(500) } Watch in the simulator and see how the value of count goes from 0 to 4. We have followed the standard convention of declaring the counter variable in the header of the for statement. You would swap with a good element i.e. Initialization expression, continuation condition, update expression So you "read" that couting down is more efficient? This leads to the following nested loop structure: Note that the bound of the inner loop varies according to the value of row, the loop counter for the outer loop. Download count1.cand read it into an Compile and run the program. Making statements based on opinion; back them up with references or personal experience. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. I think modern programmers do not understand the compiler/assembler issues much and are led to believe that all post-decrements are inefficient. There seem to be two "hidden" questions regarding unsigned wrap-around and is-looping-down-faster, but both are not clearly asked it seems. For a simple Java program where I want to make the program count from 10 to 1 by incrementing of 2 or 3 or 4 how would I change this code? Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, The future of collective knowledge sharing. Just use this method and give it the number to decrement with in param: public static void count (int counter) { for (int i = 10; i > 0; i-=counter) { System.out.println ("i = " + i); } } public static void main (String [] args) { count (2);// to decrement by 2 . It will be easier to process these structures if our loop counter also starts at 0. Here is my code but it's not working. I even pass vec by reference so that both functions access the same memory locations. The other fact that may safe cycles when counting backwards, is that when counting upwards to a non-constant value you have to have this value available in a register (or constantly reload it), while counting backwards you can compare against the constant 0. Forest: increasing horizontal separation by level bottom-up. my understanding is that it's easy to burn up to 30% of your potential CPU throughout with poor memory layout. Whether you can actually notice that difference is up for debate. If a crystal has alternating layers of different atoms, will it display different properties depending on which layer is exposed? Java code for this. You may try the following, which compiler will optimize very efficiently: Hard to say with information given but reverse your array, and count down? Any help, advice, links, push in the right direction will be accepted with open arms. True, I wasn't trying to imply that you should go ahead and do it since the compiler can't. Can a Rogue Inquisitive use their passive Insight with Insightful Fighting? how to implement countdown trigger in server side using java? If a crystal has alternating layers of different atoms, will it display different properties depending on which layer is exposed? Find centralized, trusted content and collaborate around the technologies you use most. I guess you mean decrement if you want to count down. Using two separate variables allows that.). A car dealership sent a 8300 form after I paid $10k in cash for a car. A lot of times the compiler can't make this optimization, if it can't determine that counting down will not change the observable behavior of your code. Thank you. Am I in trouble? Sometimes it is useful to use the loop variable of the outer loop as the bound for the inner loop. /** * An applet that counts down from a specified time. UPDATE: To achieve a runtime speedup with my for-loop, do I count down and if so remove the unsigned part when delcaring my int, or what other method? 592), Stack Overflow at WeAreDevelopers World Congress in Berlin, Temporary policy: Generative AI (e.g., ChatGPT) is banned. Sadly, ALGOL-M's FOR statement does not allow a negative value for STEP, so we have to use a WHILE loop if we wish to count down. Improving time to first byte: Q&A with Dana Lawson of Netlify, What its like to be on the Python Steering Council (Ep. 592), Stack Overflow at WeAreDevelopers World Congress in Berlin, Temporary policy: Generative AI (e.g., ChatGPT) is banned. Thanks for contributing an answer to Stack Overflow! Yes, you're right - admittedly, I didn't test the code. Lets dissect this example a bit. Does the US have a duty to negotiate the release of detained US citizens in the DPRK? If not, then you do not need to spend time worrying about this. Why would God condemn all and only those that don't believe in God? I don't know why there isn't an increment-compare instruction also. If a crystal has alternating layers of different atoms, will it display different properties depending on which layer is exposed? Do US citizens need a reason to enter the US? Your best bet is to get the system time when the user enters input, calculate a target system time, and check if the system time has exceeded the target system time. In the first iteration of the loop, number will be 3, number will be 7 in second iteration and so on. Asking for help, clarification, or responding to other answers. For example, if you want to print the word Hello 100 times, you can use the following while structure: In this case, the counter is the variable k, which counts from 0 through 99that is, it counts 100 times. Figure [fig-forloop] shows how the for statement works. What is the most accurate way to map 6-bit VGA palette to 8-bit? 592), Stack Overflow at WeAreDevelopers World Congress in Berlin, Temporary policy: Generative AI (e.g., ChatGPT) is banned. By clicking Post Your Answer, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct. Both sum_abs_up and sum_abs_down do the same thing and are timed they same way with the only difference being that sum_abs_up goes up memory while sum_abs_down goes down memory. The compiler is usually better at optimizing code than you are, so don't spend too much effort competing with it. The timer I'm trying to build is supposed to count down from 60 seconds. English abbreviation : they're or they're not. Such a sequence can be a list, a tuple, and many more. Physical interpretation of the inner product between two quantum states. In your particular case, you're starting the count at 20, you're continuing in the loop as long as the count is less than or equal to 0, and you're adding 1 to the count each time it loops. out. Term meaning multiple different layers across many eras? Not the answer you're looking for? array [i] = do stuff. Remember, "Premature optimization is the root of all evil". Thus, it is executed four times, which is the same number of times that line 4 is executed. The following table shows the relationship we want: If we let j be the counter for the inner loop, then j will be bound by the expression 6 \(-\) row. and Get Certified. Syntax: do { // Loop Body Update_expression } // Condition check while (test_expression); Are there any practical use cases for subtyping primitive types? Borland's Pascal compilers are notorious for performing that optimization. If "premature optimisation is the root of all evil", then the combination of premature optimisation + macros spells doom for us all. With that said, here is a style I used when programming embedded systems many years ago, when every byte and every cycle did count for something. Also, it's important to mention that with some rare loops, going down memory is sometimes faster than going up it. Making statements based on opinion; back them up with references or personal experience. How to set a timer in java in a non swing/database application. i-- is an abbreviation for i = i-1, which can be also written as i-=1. Because we have to print each rows symbols before moving on to the next row, the outer loop will count row numbers, and the inner loop will count the symbols in each row. For example, the following for statement will also print the word Hello 100 times: In fact, this for statement is equivalent to the preceding while structure. This only means that the instructions occupy less space, but not that LOOP is more efficient than a sequence of instructions. The For Loop The for loop is used to repeat a section of code known number of times. Nowadays, the compiler always knows better than you how to allocate registers. Why is a dedicated compresser more efficient than using bleed air to pressurize the cabin? Find centralized, trusted content and collaborate around the technologies you use most. Does glide ratio improve with increase in scale? When Jeremy uses the unsigned value, he has a redundant condition, does he not? EDIT, i Know this is not the best option, otherwise you should create a new class: Then you do in your code: rev2023.7.24.43543. Breaking and continuing your for loops; Use two counter in for loop; Use for loops without bodies to print the numbers 1 to 10 on the console; Counting even numbers with a for loop; Scoping out the counter variable in for loop Why do capacitors have less energy density than batteries? You issue is the counter is wrong. 592), Stack Overflow at WeAreDevelopers World Congress in Berlin, Temporary policy: Generative AI (e.g., ChatGPT) is banned. Are there any practical use cases for subtyping primitive types? Anyway, you asked about C++, not Pascal. The for statement creates a loop with 3 optional expressions: for ( expression 1; expression 2; expression 3) {. For example, consider the following pattern: Note that the number of # symbols in each row varies inversely with the row number. First of all, it is only a suggestion to the compiler, one that can be ignored. Why is there no 'pas' after the 'ne' in this negative sentence? Here, Number = 0. Maybe you should post the for loop you're using that counts down also. (I hope that makes sense). How many times is the for statement in line 2 executed? Can you help me find the problem? How do I efficiently iterate over each entry in a Java Map? Following the parenthesized list is the for loop body, which is either a single statement or a sequence of statements contained in curly brackets, {}. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. How can kaiju exist in nature and not significantly alter civilization? On the next iteration i-- > 0 fails because i == 0, so it doesn't matter that the postfix decrement rolled over the counter. Connect and share knowledge within a single location that is structured and easy to search. for (int i = 1; i < input; i++) { System.out.println (i); } Put all together: System.out.println ("Enter number to count up to: "); lastNumber = CONSOLE.nextInt (); for (int i = 1; i < lastNumber; i++) { System.out.println (i); } I . my 'i' is unsigned resgister int, also 'domain' is unsigned int. For example, if we want to print the value of the loop variable, k, after the loop completes, we have to declare it before the loop: In this example, the loop will exit when k becomes 100, so k = 100 will be printed. This makes up a part of my series. yeah i'm not able to find any clear question i could make sense of. Is it a concern? How can the language or tooling notify the user of infinite loops? "Fleischessende" in German news - Meat-eating people? You already know how to get the input. Make ordinary code look ordinary so that the special code doesn't have to compete to get attention from people reviewing, debugging, or maintaining it. Was the release of "Barbie" intentionally coordinated to be on the same day as "Oppenheimer"? What are you doing to the count variable in your for-loop? It has nothing to do with counting up or down. Is there a way to speak with vermin (spiders specifically)? Also, if you are sharing the code, please explain your code as well. Does ECDH on secp256k produce a defined shared secret for two key pairs, or is it implementation defined? This is what it my timer should do: All I need to know is how to make it countdown. A much safer loop bound in this case would be k \(<\)= 100. Can a Rogue Inquisitive use their passive Insight with Insightful Fighting? Making statements based on opinion; back them up with references or personal experience. The body of the inner loop is executed 36 times9 times for each execution of line 2. How has it impacted your learning journey? In this case, progress toward the loop bound is made by decrementing the loop counter: Note in this case that we are using unit indexing instead of zero indexing, because countdowns repeat, or iterate, from 10 down to 1, not from 10 down to 0. Can a creature that "loses indestructible until end of turn" gain indestructible later that turn? How to avoid conflict of interest when dating another employee in a matrix management company? Correct? They're absolutely right. It is simple to countdown with Java. When the system time exceeds your target system time, then break out of the loop. This restricts the variables scope to the for statement itself. These forms were useful for me on the particular CPUs and compilers that I was using, but your mileage may vary. "Fleischessende" in German news - Meat-eating people? In computer programming, loops are used to repeat a block of code. Otherwise you are right, in this manner (without a 'sleep/pauze' like a recursive setInterval(f,t), the element cco will only have 0 visible. Is it possible to split transaction fees across multiple payers? Consider using a sleep function and have it sleep 1 second between each iteration and display the seconds left. Get the starting system time and calculate your target system time. When it reaches 00:00, * it optionally plays a sound and optionally moves the browser to a new page. This makes decrementing loops more efficient than incrementing ones. It still pauses, when i press the start button the button don't even go up until the timer is done! This is saying start at count = 20, until count is less or equal to zero, add 1 to count each time. There are many ways to do this. The variable k in this example is called a or loop counter. For example, suppose you are working for Giant Auto Industries, and your boss wants you to print a table for buyers to figure the cost of buying multiple quantities of a certain part. Not the answer you're looking for? The code given by Don will be vert efficient. In the circuit below, assume ideal op-amp, find Vout? The for loop is executed in exactly the same way as the original code: The initialization part is executed once, before the loop begins. Because you know the exact number of times the loop repeats beforehand, a counting loop can be made dependent on the value of a counter. The condition is evaluated. By clicking Post Your Answer, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct. System.out.format("\n Number of Digits in a Given Number = %d", Count); The output of given variable 1465 is 4. The value of the loop control variable is often used in the body of the loop. In Java, I have the following for loop and I am learning Python: A Holder-continuous function differentiable a.e. Java Program to Count Number of Digits in a Number using For Loop Hi I'm trying to create a simple countdown. Connect and share knowledge within a single location that is structured and easy to search. Note that we start counting from 0 instead of 1. Can you help me find the problem? Some examples: Unknown number of times: "Ask the User to Guess a pre-determined number between 1 and 100". Should I trigger a chargeback? The compiler transforms this code: into an internal representation more akin to this: (I say notorious not because the optimization affects the outcome of the loop, but because the debugger displays the counter variable incorrectly. Everyone here is focusing on performance. Well, compared to algorithm structure memory layout is also a micro-optimization, isn't it? purposes. Most caches are optimized for going up memory, not down memory. Lets say you want to countdown 10 min so Try this. How long do I keep going? Connect and share knowledge within a single location that is structured and easy to search. A loop bound is a value that controls how many times a loop is repeated. If compiler completely respected the "register" hint, it would probably result in a perf degradation. Answer: Here is a java example of a count down loop: Source: (Example.java) public class Example { public static void main (String[] args) { for (int i = 10; i > 0; i --) { System. A loop that counts down from 10 to 0 will always terminate, it should never become an infinite loop, and you should be able to write it without using a break, which is, again, for extraordinary situations only. Here is my code, any help is really appreciated! Airline refuses to issue proper receipt. @foljs: No--memory layout can have a huge (1000x or more) effect because the memory hierarchy has such a huge disparity in access speeds. * This class demonstrates most applet methods and features. I'm working on a school project in Java and need to figure out how to create a timer. What value will j have when the following loop. If we let row be the row number, then in each row we want to print 6 \(-\) row symbols. By iterating end to 0 we know that the element at the end of the array has already been proven valid for this iteration. Console? I'll emphasize again that whether these forms are a win for you depends on the CPU and compiler that you're using. Using robocopy on windows led to infinite subfolder duplication via a stray shortcut file. How can I avoid this? no way of knowing how many guesses it will take. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Michael's answer shows why x86 gives you a comparison with zero as an implicit side effect of many instructions, so after you adjust your counter, you just branch based on the result instead of doing an explicit comparison. You'll see people using the Timer class to do this. That said, better spent optimization time would be on thinking about the overall program structure, data structures and algorithms used, resource utilization, etc. C++ "for" loops aren't quite as easy to apply that optimization to as Pascal "for" loops are because the bounds of Pascal's loops are always fully calculated before the loop runs, whereas C++ loops sometimes depend on the stopping condition and the loop contents. Find centralized, trusted content and collaborate around the technologies you use most. Since memory access time is the bottleneck that most programs today face, this means that changing your program so that you go up memory can result in a performance boost even if this requires comparing your counter to a non-zero value. The following method contains a countdown loop, which prints 10 9 8 7 6 5 4 3 2 1 BLASTOFF. (Maybe other architectures do that, too; I don't know.). If the program is stuck in a loop that generates output, it will be obvious that it is looping, but if no output is being generated, the computer will appear to freeze, no longer responding to your keyboard or mouse commands. Loops in Java come into use when we need to repeatedly execute a block of statements. My point is, I could design an architecture or compiler that breaks this Also, what are you even doing that requires such a ridiculous optimization? Thus, in row 1 we want five symbols; in row 2 we want four symbols; and so on. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Again, paste the output copy or screen shot after each one. Could ChatGPT etcetera undermine community by making statements less significant for us? Because all these values are odd, k will never equal 100. Instead you should post the code as you had done so I've rolled back. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. If it has, then break out of the loop. This second form takes advantage of pointer (address) arithmetic. The loop body consists of a single print() statement: The next example prints the sequence 5, 10, 15, \(\dots\) 50, but it uses several statements within the loop body: In this example, the scope of the local variable m, declared within the loop body, is limited to the loop body and cannot be used outside of that scope. This may solve the current issue but does not solve any larger problems. Connect and share knowledge within a single location that is structured and easy to search. It is simple to countdown with Java. I'm guessing your backward for loop looks like this: In that case, because i is unsigned, it will always be greater than or equal to zero. /* NetRexx */ options replace format comments java crossref savelog symbols nobinary say say 'Loops/Downward for' loop i_ = 10 to . You have. Don't do anything fancy in the name of performance until testing and profiling show it to be necessary. Here, the value of sum is 0 initially. Using a nested for loop to count up and down. The first part initializes the loop variable, the second part tests some condition, and the third part increments or decrements the loop variable. If we set the test expression in such a way that it never evaluates to false, the for loop will run forever. Enhanced for loop provides a simpler way to iterate through the elements of a collection or array. Having trouble with count controlled for loop, Counting and displaying distinct integers from user, Issues with counter and for loop. minimalistic ext4 filesystem without journal and other advanced features. It's also unnecessary, as far as I can tell. Is it a concern? How can kaiju exist in nature and not significantly alter civilization? The last System.out.format statement prints the number of digits in that number. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Concern yourself with the bigger picture of memory layout and algorithm structure instead of trivial micro-optimisations. How to count down in for loop? rev2023.7.24.43543. We also acknowledge previous National Science Foundation support under grant numbers 1246120, 1525057, and 1413739. Can somebody be charged for having another person physically assault someone for them? i-=2 is an abbreviation for i = i-2
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