Processing 1.0 - Processing Discourse - weird for loop i++ overflow

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weird for loop i++ overflow (Read 840 times)

alphachapmtl

weird for loop i++ overflow
Nov 16^th, 2007, 7:53am

I had a weird error in a bigger program, which I finally chased down to the following piece of code:

void setup() {
size(120,120);
noLoop();
//
int k1=2147483646;
int k2=2147483647;
for (int k=k1; k<=k2; k++) println("k="+k);
//
}//setup()

void draw() {
}//draw()

(k1 and k2 are valid integers, the loop should print k1 and k2 and stop,
but when k++ is evaluated, k goes from 2147483647 to -2147483648, and the loop goes on)

antiplastik

Re: weird for loop i++ overflow
Reply #1 - Nov 16^th, 2007, 9:49am

k1 and k2 are valid integers but k2+1 is not, since the integer limit is 2147483647. k2+1 will return -2147483648, which is the lowest limit of an integer.

Code:

int k = 2147483647;
println(k+1);

Since k can't go further than k2 in your loop, k <= k2 is always true. You have to declare k as a 'long' variable to make it work :

Code:

for (long k=k1; k<=k2; k++) println("k="+k);

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