I can't seem to figure out why this is an infinite loop in python??
for i in range(n):
j=1
while((i*j)<n):
j+=1
shouldn't the outer loop go n times. incrementing j until its equal to n div i each time?
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9 Answers
i starts at 0, so the while condition stays always true; see the range docs for details.
Comments
You can create a "trace" showing the state changes of the variables.
- n= 5; i= 0
- n= 5; i= 0; j= 1
- i*j < n -> 0 < 5: n= 5; i= 0; j= 2
- i*j < n -> 0 < 5: n= 5; i= 0; j= 3
- i*j < n -> 0 < 5: n= 5; i= 0; j= 4
- i*j < n -> 0 < 5: n= 5; i= 0; j= 5
- i*j < n -> 0 < 5: n= 5; i= 0; j= 6
etc.
You can prove that your trace is correct by inserting print statements.
When in doubt, print it out.
1 Comment
Jesvin Jose
and use the logging module in bigger programs. You need to modify just one line to change the verbosity
i starts at zero, so the condition for the inner loop is always 0*j < n, which will always be true.
Comments
Because the initial value of i is 0.
Comments
The first value in i will be 0. 0 times anything is 0.
answered Jan 12, 2010 at 17:42
Ignacio Vazquez-Abrams
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Comments
because i is 0!! and i*j=0
Comments
range(n) starts at 0, not 1. 0 * j will always be less than n.
Comments
On the first time through the outer loop, the inner loop becomes an infinite loop. It doesn't matter what happens after that. There's no "after infinity".
Comments
i is 0 rewrite you loop like
for i in range(1,n):
j=1
while((i*j)<n):
j+=1
using this version of the range function will create a range that starts at 1 instead of 0
