for loop index variable

[Guest]

(I tried to post this earlier, but it seems without success)

A similar question to this has been answered many times, to whit the
question applying when the index variable of a for loop is declared in
the loop header, but this time that isn't the case:

I've got a piece of code a bit like this:

#include <iostream>
#include <cmath>

for (x=0; x<digits; x++)
{
//do something dependent on the value of x
}

//Depending on the value of x after one of these
//loops, I cd do the last step better outside the loop?

What is the value of x when the loop terminates? Is it indeed digits,
as one would expect? Does it reset to 0? Could it be anything
depending on my implementation?

Thanks,

James M.

 

[Jonathan Mcdougall]

(I tried to post this earlier, but it seems without success)

A similar question to this has been answered many times, to whit the
question applying when the index variable of a for loop is declared in
the loop header, but this time that isn't the case:

I've got a piece of code a bit like this:

#include <iostream>
#include <cmath>

for (x=0; x<digits; x++)
{
//do something dependent on the value of x
}

//Depending on the value of x after one of these
//loops, I cd do the last step better outside the loop?

What is the value of x when the loop terminates? Is it indeed digits,
as one would expect? Does it reset to 0? Could it be anything
depending on my implementation?

A for loop is not "magical". It has three sections: initialization,
condition, expression. The initializaition is done once before the loop
begins, the condition is checked at each loop (including before the
first one) and the expression is evaluated after the first loop and in
subsequent loops.

Whatever you write in these sections is what happens. If you write

for (x=0; x<digits; ++x)
{
}

it's the same thing as

x=0;
for(;
{
if (x>=digits)
break;

++x;
}

So when the loop ends (if it does), you are assured that x>=digits.


Jonathan

 

[John Carson]

(I tried to post this earlier, but it seems without success)

A similar question to this has been answered many times, to whit the
question applying when the index variable of a for loop is declared in
the loop header, but this time that isn't the case:

I've got a piece of code a bit like this:

#include <iostream>
#include <cmath>

for (x=0; x<digits; x++)
{
//do something dependent on the value of x
}

//Depending on the value of x after one of these
//loops, I cd do the last step better outside the loop?

What is the value of x when the loop terminates? Is it indeed digits,
as one would expect? Does it reset to 0? Could it be anything
depending on my implementation?

You don't show the declaration of x. If your code is really:

int x;

for (x=0; x<digits; x++)
{
//do something dependent on the value of x
}

then x will equal digits immediately after the loop (there is no resetting
to zero) --- assuming that there is no break; or goto; statement inside the
loop that could terminate it prematurely and no code inside the loop that
alters the value of x (e.g., x = digits +10.

 

[Peter Julian]

(I tried to post this earlier, but it seems without success)

A similar question to this has been answered many times, to whit the
question applying when the index variable of a for loop is declared in
the loop header, but this time that isn't the case:

I've got a piece of code a bit like this:

#include <iostream>
#include <cmath>

for (x=0; x<digits; x++)
{
//do something dependent on the value of x
}

//Depending on the value of x after one of these
//loops, I cd do the last step better outside the loop?

What is the value of x when the loop terminates? Is it indeed digits,
as one would expect? Does it reset to 0? Could it be anything
depending on my implementation?

It depends where x was declared, something you failed to show in your
example.

Assuming that int x; was indeed declared outside the loop, x will hold
whatever value the conditional expression "failed" with (x<digits).
So x == digits following the loop if x++ is its only modifier.

The key here is scope, where was x declared?