Difference between the outputs.

[psaikia]

I am new to C programming. Please , tell me , why there is difference between the outputs of the two programs below.

 #include<stdio.h>
int main()
{
  int i=0,j=0;




  for(;i<=20;i++)
     {
         for(;j<=10;j++)
            {
                     printf("%d\t%d\n",i,j);
            }


     }
     return 0;
  }

 #include<stdio.h>
int main()
{
  int i,j;




  for(i=1;i<=20;i++)
     {
         for(j=1;j<=10;j++)
            {
                     printf("%d\t%d\n",i,j);
            }


     }
     return 0;
  }

[mnd22]

Because i and j is initialized with different values.

Does this looks different?

Code 1:
i = 0
j = 0

Code 2:
i = 1
j = 1

[psaikia]

That is ok

But the outer loop is not working in the first one . ,, In the second one the outer loop and inner loop is working.

[sparkomemphis]

That is ok

But the outer loop is not working in the first one . ,, In the second one the outer loop and inner loop is working.

In the first example, What is the initial value of j when i > 0 ?

[psaikia]

In the first example, What is the initial value of j when i > 0 ?

Did not understand , what are you trying to mean,plz elaborate.

[mnd22]

This one got me too @@, The inner loop on the first code will only work once. j needs to be reinitialized to 1 or 0 on the inner loop so it will work properly.

[psaikia]

This one got me too @@, The inner loop on the first code will only work once. j needs to be reinitialized to 1 or 0 on the inner loop so it will work properly.

Yeah you are correct ,In the 1st code if we reinitialize the j in second loop , it works.

Can you explain me why it is like this ? thank you.

[CommonTater]

Yeah you are correct ,In the 1st code if we reinitialize the j in second loop , it works.

Can you explain me why it is like this ? thank you.

What is the value of j after the first pass through the inner loop?

Since the first example (stupidly) removes the initializer from the for loops and places them outside both loops, the value of j will stay wherever the inner loop left it the first time through... Second time, j = 11... the loop does not run.

I've seen this broken format of for loops quite frequently over the past few weeks. Your code demonstrates perfectly why it's broken!

[mnd22]

Your condition checks if j is <= 10. After the first loop j is 11 so without setting it to 0 again the result will always be false.

It's a pretty simple code you should try running it through your mind or if you have a good IDE try stepping through the code in debug mode.

[psaikia]

Yeah , now I understand , Thank you ​commontater and mnd22