Turning a nested for loop into a nested while loop fails - why?

**Placebo** · 04-07-2019

Hi!

As an exercise I would like to turn following nested for loop into a nested while loop:

Turning a nested for loop into a nested while loop fails - why?-nested_forloop-png

Turning a nested for loop into a nested while loop fails - why?-nested_forloop-png

But somehow it does not work out the way I want it to and obviously after all iterations are completed within the inner while loop,
my program does not find its way back into the outer while loop to start over again:

Turning a nested for loop into a nested while loop fails - why?-nested_whileloop-png

Turning a nested for loop into a nested while loop fails - why?-nested_whileloop-png

Code:

#include <stdio.h>

 int main() {
     int i = 1, j = 1;
     while(i <= 5) {
        while(j <= 5) {
            printf("%4d", i * j);
            j++;
        }
        printf("\n");
        i++;
     }


     return 0;
 }

I cannot spot my mistake and would appreciate any help.^^

regards,
Placebo

**laserlight** · 04-07-2019

Your j = 1 is in the wrong spot. Remember j is used in the inner loop.

**Placebo** · 04-07-2019

Hey,

thanks a lot, your hint helped me out:

Turning a nested for loop into a nested while loop fails - why?-nested_whileloop-png

The problem is though that I do not understand why we must assign the value directly before the inner loop begins, i.e. directly before we will need the variable?
Can't the program remember the value of the variable j, when I would have assigned it at the very beginning of the program and then start using the remembered value whenever it is needed?
Is this a particularity with "loop-blocks" or with any seperated blocks or scopes, in general?

**laserlight** · 04-07-2019

It is doing that: it "remembers" the value of j, and that's the value of j that was incremented again and again in the inner loop. That value of j is no longer 1, which is why you have to "reset" it before the inner loop.

**Salem** · 04-07-2019

Remember that

Code:

for ( a ; b ; c ) {
    d;
}

Is approximately equal to

Code:

a;
while ( b ) {
    d;
    c;
}

The approximation breaks down when trying to use the 'continue' keyword.

**Placebo** · 04-07-2019

Originally Posted by laserlight

It is doing that: it "remembers" the value of j, and that's the value of j that was incremented again and again in the inner loop. That value of j is no longer 1, which is why you have to "reset" it before the inner loop.

Ah, now I indeed got it - thanks a lot!

Also, thanks Salem for your hint.^^

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