Thread: Can some one help me understand the logic of this beginner's program

The code:

Code:

#include<stdio.h>

int main()
{

    int j ;
    while ( j <= 10 )
    {
        printf ( "\n%d", j ) ;
        j = j + 1 ;
    }

    return 0;
}

Output:

2
3
4
5
6
7
8
9
10

I am using Code Blocks and what I do not understand is that while in the program no particular value has been assigned to integer j, why does the output start with 2, as if the value of j is 2 in the beginning?

Thanks in advance.

Since j is a local variable it can take any value. Either you have to initialize it with 0 or make it a global variable.

Hi Satya,

Thank you for taking time to reply to my query. So can I say, that without declaring j as a global variable or by not assigning a value to J in the beginning - the outcome of this program will not be reliable, and that different outcome can arise with different compilers?

Yes.

j is an uninitialized local (non-global) variable, and therefore this is really an invalid program and its output is undefined. It could crash your computer, or print 2. Why C allows uninitialized local variables is questionable (for example, Java does not allow an uninitialized local variable before it is used.. however, programmers often resort to initializing to null, which doesn't help much, when you get a NullPointerException). The solution is up to the programmer to always initialize his or her variables to sane default value

Originally Posted by MacNilly

j is an uninitialized local (non-global) variable, and therefore this is really an invalid program and its output is undefined. It could crash your computer, or print 2. Why C allows uninitialized local variables is questionable (for example, Java does not allow an uninitialized local variable before it is used.. however, programmers often resort to initializing to null, which doesn't help much, when you get a NullPointerException). The solution is up to the programmer to always initialize his or her variables to sane default value

Thanks for the answer Macnilly.