Why first for loop is infinite loop after adding second for loop

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1.00/5 (1 vote)

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C++

int main()
{
	int x(5),a[7],i(0);

	for(i=0;i<8;i++)
	{
        a[i] = 0;
        cout << "i=" << i <<endl;
        cout << "a[" <<i <<"]=" <<a[i]<<endl;
	}
	for(i=7;i>=0;i++)
	{
		a[i]=x%2;
		cout << "a[" <<i <<"]=" <<a[i]<<endl;
		x=x/2;
		if(x<2)
		{
			i--;
			a[i]=x;
			break;
		}
	}

}

Posted 18-Aug-15 19:50pm

the_beginner

Updated 18-Aug-15 20:09pm

Sergey Alexandrovich Kryukov

v2

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Sergey Alexandrovich Kryukov 19-Aug-15 2:11am

To start with, always declare loop variables inside "for". Never use your externally defined "i" as a loop variable. Use the debugger.
—SA

CPallini 19-Aug-15 2:27am

You should also check
for(i=7;i>=0;i++)
it doesn't look correct.

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OriginalGriff · Accepted Answer · 2015-08-18T20:11:00

Solution 1

Look at your code:

int x(5),a[7],i(0);

for(i=0;i<8;i++)
{
a[i] = 0;
...
}

So your array a has 7 elements, and you write 0 into the first 8.
When you write the 8th element, it overruns the array, and writes into the next memory location - which contains the variable i. So after the 8th time round the loop, it looks at i and sees it is zero, so it goes round again... And again...

Posted 18-Aug-15 20:11pm

OriginalGriff

Comments

the_beginner 19-Aug-15 2:19am

Thanks

OriginalGriff 19-Aug-15 2:32am

You're welcome!

CPallini 19-Aug-15 2:24am

5.