# For loops vs. While loops

797 views (last 30 days)
Joe on 12 Mar 2013
Answered: Roman Sustaita on 18 Nov 2019
I know the two loops are used differently, although they could be used for the same purpose. However, how would you generally know which one to use, especially in cases where one over the other would be valid?

Jan on 12 Mar 2013
Edited: Jan on 12 Mar 2013
The FOR loop is nicer and more compact, if the number of iterations is known before the loop is started. The WHILE loop is nicer, when the number of iterations is determined inside the loop.
Compare:
for k = 1:10
disp(k);
end
with:
k = 1;
while k <= 10
disp(k);
k = k + 1;
end
On the other hand:
a = 1e6;
while a > 1
a = a * rand;
end
with this (1e8 is an arbitrary large guess - a bad idea!):
a = 1e6;
for k = 1:1e8 % Ugly, although it is not created explicitly
a = a * rand;
if a <= 1
break;
end
end
There are some overlaps, e.g. running an iteration until a certain number of loops or a specific criterion is reached. Then usually WHILE is preferred with the convergence limit as test, because this reflects the main character of the loop, while the limitation of iterations is a fallback mechanism only.

#### 1 Comment

Jos (10584) on 22 Feb 2019
The infinite for loop syntax is also nice to know:
for k=0:1e5:Inf,
if k > 1e6
break
end
disp(k)
end

Roman Sustaita on 18 Nov 2019
Calculate the area of a circle using a for and while loop