Noob 'if' statement problem

[now]

Hey Guys.

I'm not sure whats going on here. I can't get my head around it but the if loop doesn't seem to like looping more than 8 times >.<

I have a simple program that i want to use to draw a block of characters on the terminal. First it initializes a multi-dimensional array, 1 dimension for x, 1 for y. Next it goes through an if loop to assign the char # to each part of the array. But in this loop somewhere something goes wrong because wall[8][9] and wall[9][0] both end up equaling '?' and wall[9][1] - wall[9][9] equal ''. :S
I'm very confused. Anyway here is the code:

#include <iostream>

using namespace std;

int main(){

char wall[9][9];

for (int a=0;a <= 9; a++){
for (int b=0;b <= 9; b++){
   wall[a][b] = '#';
}
}

for (int a=0;a <= 9; a++){
for (int b=0;b <= 9; b++){
   cout << wall[a][b];
}
   cout << endl;
}

return 0;

}

and this is the output i get when i run it:

##########
##########
##########
##########
##########
##########
##########
##########
#########$
$
	

BUT! If i run this code:

#include <iostream>

using namespace std;

int main(){

char wall[10][10];

for (int a=0;a <= 9; a++){
for (int b=0;b <= 9; b++){
   wall[a][b] = '#';
}
}

for (int a=0;a <= 9; a++){
for (int b=0;b <= 9; b++){
   cout << wall[a][b];
}
   cout << endl;
}

return 0;

}

I get the expected block of chars:

##########
##########
##########
##########
##########
##########
##########
##########
##########
########## 

I'm not sure what i'm doing wrong >.< but if someone can slap me on the wrist and point me in the right direction, i'll be more than happy.

Cheers,
now.

[z05DSL3A]

Your for loops should not use <= only <.

#include <iostream>

using namespace std;

int main(){

    char wall[9][9];

    for (int a=0;a < 9; a++){
        for (int b=0;b < 9; b++){
            wall[a][b] = '#';
        }
    }

    for (int a=0;a < 9; a++){
        for (int b=0;b < 9; b++){
            cout << wall[a][b];
        }
        cout << endl;
    }

    return 0;

}

[rossipoo]

There is nothing wrong with using the <= but you must realize that it is inclusive with 9. That means the for loop is going from 0 to 9, which is 10 times. Your array only has 9 slots in it.

The solution is to either, like you realized, increase the size of your array to 10, or to change the for loop so it goes from 0 to 8 (nine times). You could do this either by using a < instead, or changing the expression to a <= 8.

[z05DSL3A]

The solution is to either, like you realized, increase the size of your array to 10...

What kind of a solution is that? I need an array with nine elements in it, so I best make it ten because I'm not going to work within the bounds correctly.

You can, technically, use <= in a for loop. However, when working with arrays inside the the loop it is easier an less error prone to just use <.

int main()
{
    enum {arraySize = 9}; // or some other constant inegral

    int anIntArray[ arraySize ];

    int i(0);
    for (i = 0; i < arraySize; ++i)
    {
        anIntArray[i] = i;
    }

    // The following dose the same
    for (i = 0; i <= arraySize - 1; ++i)
    {
        anIntArray[i] = i;
    }
    
    return 0;
}

[now]

Correct me if i'm wrong but is not.

int array[9]

Initialising an array of size 10? Thats why i thought <= should work. I will try just using < from now on in if statements to see if that works. Thanks for the replies guys :)

[Hammurabi]

Nope. The number doesn't represent the highest index but the total number of elements (the size). So if you want 10 elements, you must use int array[10];.

[now]

Ah, fair enough than. Thanks for clearing that up ^.^
Should be fine now.