Questions tagged [while-loop]
A while loop is a control structure used in many programming languages to continuously execute a set of instructions as long as a particular condition is met.
24,212
questions
998votes
19answers
1.6mviews
How to emulate a do-while loop?
I need to emulate a do-while loop in a Python program. Unfortunately, the following straightforward code does not work:
list_of_ints = [ 1, 2, 3 ]
iterator = list_of_ints.__iter__()
element = None
...
- 36.7k
755votes
14answers
834kviews
Syntax for a single-line while loop in Bash
I am having trouble coming up with the right combination of semicolons and/or braces. I'd like to do this, but as a one-liner from the command line:
while [ 1 ]
do
foo
sleep 2
done
- 20.2k
644votes
5answers
264kviews
Why is “while ( !feof (file) )” always wrong?
What is wrong with using feof() to control a read loop? For example:
#include <stdio.h>
#include <stdlib.h>
int
main(int argc, char **argv)
{
char *path = "stdin";
FILE ...
- 188k
607votes
23answers
94kviews
Which is faster: while(1) or while(2)?
This was an interview question asked by a senior manager.
Which is faster?
while(1) {
// Some code
}
or
while(2) {
//Some code
}
I said that both have the same execution speed, as the ...
- 4,621
369votes
12answers
232kviews
Else clause on Python while statement
I've noticed the following code is legal in Python. My question is why? Is there a specific reason?
n = 5
while n != 0:
print n
n -= 1
else:
print "what the..."
- 24.8k
312votes
13answers
696kviews
How do I plot in real-time in a while loop using matplotlib?
I am trying to plot some data from a camera in real time using OpenCV. However, the real-time plotting (using matplotlib) doesn't seem to be working.
I've isolated the problem into this simple ...
- 8,663
304votes
6answers
175kviews
How can you run a command in bash over and over until success?
I have a script and want to ask the user for some information, but the script cannot continue until the user fills in this information. The following is my attempt at putting a command into a loop to ...
- 10.4k
285votes
34answers
133kviews
Are loops really faster in reverse?
I've heard this quite a few times. Are JavaScript loops really faster when counting backward? If so, why? I've seen a few test suite examples showing that reversed loops are quicker, but I can't find ...
- 64.8k
272votes
5answers
425kviews
How to check if all elements of a list match a condition?
I have a list consisting of like 20000 lists. I use each list's 3rd element as a flag. I want to do some operations on this list as long as at least one element's flag is 0, it's like:
my_list = [["a"...
- 25.5k
265votes
20answers
170kviews
Declaring variables inside or outside of a loop
Why does the following work fine?
String str;
while (condition) {
str = calculateStr();
.....
}
But this one is said to be dangerous/incorrect:
while (condition) {
String str = ...
- 56.8k
245votes
8answers
215kviews
A variable modified inside a while loop is not remembered
In the following program, if I set the variable $foo to the value 1 inside the first if statement, it works in the sense that its value is remembered after the if statement. However, when I set the ...
- 3,013
229votes
3answers
17kviews
Java method with return type compiles without return statement
Question 1:
Why does the following code compile without having a return statement?
public int a() {
while(true);
}
Notice: If I add return after the while then I get an Unreachable Code Error.
...
- 24.3k
225votes
21answers
201kviews
Are "while(true)" loops so bad? [closed]
I've been programming in Java for several years now, but I just recently returned to school to get a formal degree. I was quite surprised to learn that, on my last assignment, I lost points for using ...
- 3,824
190votes
15answers
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How can I make sense of the `else` clause of Python loops?
Many Python programmers are probably unaware that the syntax of while loops and for loops includes an optional else: clause:
for val in iterable:
do_something(val)
else:
clean_up()
The body ...
- 45.9k
190votes
2answers
243kviews
How to break out of a loop in Bash?
I want to write a Bash script to process text, which might require a while loop.
For example, a while loop in C:
int done = 0;
while(1) {
...
if(done) break;
}
I want to write a Bash script ...
- 6,125