Unable to assign values to an array

Question

Look at this piece of code.. In this I am taking input from a file and assigning to an array sudoku[][].. and simultaneously assigning those values to TempArr[][] (another array)..

But when I checked the values of TempArr[][] after assigning, there aren't same as in sudoku[][].

for (i=0;i<size;i++)
{
    for (j=0;j<size;j++)
    {
        if(fscanf(ip_file,"%d",&sudoku[i][j])==1)
        {         
                  //copy to TempArr
                  TempArr[i][j]==sudoku[i][j];
        }
        else
        {
            perror ("fscanf failed on input file.\n");
            // return error
        }
    }
}

So, when I replaced "sudoku[][]" with "TempArr[][]", its working.. i.e., if(fscanf(ip_file,"%d",&TempArr[i][j])==1)

Why this is happening and how do I handle this situation ?

Don't you get an expression has no effect kind of warning for that? — K-ballo
– K-ballo, Commented Nov 16, 2011 at 17:37
@K-ballo - it does if you're using -Wunused-value (or -Wall) with gcc, but otherwise ... not so much. However, it's a good point to make - thanks, editing. — Brian Roach
– Brian Roach, Commented Nov 16, 2011 at 20:34

Brian Roach · Accepted Answer · 2011-11-16 20:38:10Z

5

TempArr[i][j]==sudoku[i][j];

See the == ? That wouldn't be assigning ;)

Edit: Also worth noting - the compiler can help you with these things. If you use the -Wall option when compiling, it will tell you:

> gcc -Wall -o test test.c
test.c:13:9: warning: statement with no effect [-Wunused-value]

There's a number of helpful warning levels you can specify to alert you of these things:

http://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html

edited Nov 16, 2011 at 20:38

answered Nov 16, 2011 at 17:33

Brian Roach

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5 Comments

user1027046 Over a year ago

Thanks, I wasn't looking at that small mistake

Martin James Over a year ago

Should there not be a warning for comparisons where the result is ignored? I'm sure I got one last time I did this on gcc. It's such a common error, (we've all done it), that there should be a warning.

Hot Licks Over a year ago

Some compilers warn of a result with no side-effect or use. And Java will not let you do the opposite (use = instead of ==) due to the way they type the values.

Brian Roach Over a year ago

Not unless you specifically ask for them. It's a good point to make though, so I've added that to my answer.

user1027046 Over a year ago

I didn't get any warning. I'm using Mingw

Hot Licks · Accepted Answer · 2011-11-16 17:34:10Z

1

Uh, == isn't assignment, it's a test for equality.

answered Nov 16, 2011 at 17:34

Hot Licks

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2 Comments

Hot Licks Over a year ago

(I've made the same mistake more than once -- probably more often than I've tried to use = for comparison.)

Brian Roach Over a year ago

I loath admitting it, but same here.

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