1. ## diagonals

supose theres an array SIZE X SIZE
the user enter coaordinate (a,b)
i want to put 9 in each coardinate on the 2 diagonals that including (a,b).

this is my try :

Code:
```//////  diagonal I  {/}  ////

// UP
for(i=a-1, j=b+1; (0<=i)||(j<SIZE-b); i--,j++)
board[i][j]=9;

// DOWN
for(i=a+1,j=b-1; (i<SIZE-b)||(0<=j); i++,j--)
board[i][j]=9;

//////  diagonal II  {\}  ////

// UP
for(i=a-1,j=b-1; ((0<=i)||(0<=j)); i--, j--)
board[i][j]=9;

// DOWN
for(i=a+1,j=b+1; ((i<SIZE-1)||(j<SIZE-1)); i++, j++)
board[i][j]=9;```

2. Code:
```//////  diagonal I  {/}  ////

// UP-RIGHT
for(i=a-1, j=b+1; (0<=i) && (j<SIZE); i--,j++)
board[i][j]=9;

// DOWN-LEFT
for(i=a+1,j=b-1; (i<SIZE) && (0<=j); i++,j--)
board[i][j]=9;

//////  diagonal II  {\}  ////

// UP-LEFT
for(i=a-1,j=b-1; ((0<=i) && (0<=j)); i--, j--)
board[i][j]=9;

// DOWN-RIGHT
for(i=a+1,j=b+1; ((i<SIZE) && (j<SIZE)); i++, j++)
board[i][j]=9;```
You need AND not OR. You want both conditions to be true, to make sure none of the axis goes out of bounds.
Don't know why you had SIZE-a or SIZE-b. You just check them to be <=SIZE-1 or <SIZE (same thing).
Last note, you don't include (a,b). You start with i=a+1 or i=a-1 and j=b+1 or j=b-1. Never i=a or j=b. You could change that if that is what you want.