Printing a 2D Array using pointers pointing to pointers that point to the array

Question

I'm trying to print a multiplication table that is stored in a 2D array by using pointers to pointers. When I run this code, it only prints out the "1s" column. If I remove the outer loop's incrementation and the line break conditional, then it will print the numbers 1-10 ten times. I don't understand this behavior.

printf("\n");
printf("Multiplication Table in standard array syntax\n");

int a[10][10];
int j;
int k;
int prod;
for (j = 1; j < 11; j++){
    for (k = 1; k < 11; k++){
        prod = j*k;
        a[j - 1][k - 1] = prod;
        printf("%d ", a[j - 1][k - 1]);
        if (k == 10)
            printf("\n");
    }
}

printf("\n");
printf("Multiplication Table in standard + pointer syntax\n");

int *pi[10];
int x;
for (x = 0; x <10; x++){
    pi[x] = a[x];
}

int y;
for (x = 0; x < 10; x++){
    for (y = 0; y < 10; y++){
        printf("%d ", *(pi[x] + y));
        if (y == 9)
            printf("\n");
    }
}

printf("\n");
printf("Multpilication Table in pure pointer syntax\n");

int **ppi;
ppi = pi;
int p;
int q;
for (p = 0; p < 10; p++){
    for (q = 0; q < 10; q++){
        printf("%d", *(*ppi + q));
        if (q = 9)
            printf("\n");
    }
    ppi++;
}

}

@Gone What is about that code?

Grijesh Chauhan
– Grijesh Chauhan

2014-02-14 17:54:38 +00:00
Commented Feb 14, 2014 at 17:54 — Grijesh Chauhan
– Grijesh Chauhan, Commented Feb 14, 2014 at 17:54

G one · Accepted Answer · 2014-02-14 17:46:25Z

2

The only typo is if (q = 9)

Change it to if (q == 9) as that is terminating your loop

edited Feb 14, 2014 at 17:46

answered Feb 14, 2014 at 17:36

G one

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5 Comments

Grijesh Chauhan Over a year ago

there is not mistake?

Grijesh Chauhan Over a year ago

In which question? What line?

Christian Baker Over a year ago

Thanks, I know that's how I'm supposed to set it up, but I make that mistake so often :P

G one Over a year ago

:) Weekend has something to do with it i guess ;)

Grijesh Chauhan Over a year ago

@Gone :D No I am not drunk :P

Ronny Lindner · Accepted Answer · 2014-02-14 17:39:45Z

1

the first 2 blocks are working fine, in the third block you have q = 9 instead of q == 9 (as gregkow said). There is a coding style for if-clauses (called Yoda Conditions) thas has the value first:

if( 9 == q )

This would fail on a typo like this:

if( 9 = q )
main.c: In function 'main':
main.c:51:15: error: lvalue required as left operand of assignment
     if (9 = q)
           ^

answered Feb 14, 2014 at 17:39

Ronny Lindner

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Comments

gregkow · Accepted Answer · 2014-02-14 17:32:51Z

0

I would suspect the if (q = 9) line. C has no problem with this (it sets q equal to 9 and then checks if nonzero). This would likely both end your for loop early and print new lines.

answered Feb 14, 2014 at 17:32

gregkow

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