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macOS C Array Setting Fractions

D

Duke Leto

macrumors regular
Original poster
Mar 17, 2008
166
0
I have a class containing a few arrays a,b, and c. These are double values.
Code: 
@interface ArrayContainer : NSObject 
{
	double a[10][10];
	double b[10][2];
	double c[10];
}
However, when I set the values to fractions, it is still 0!
Code: 
...
a[2][1] = 1/5;
...
But if I set them directly, it works!
Code: 
...
a[2][1] = .2;
...
Why don't these arrays work!?
 
lee1210

lee1210

macrumors 68040
Jan 10, 2005
3,182
3
Dallas, TX
the token 1 is interpreted as an int with the value 1. 5 is the same. .2 is a double with the approximate value of .2. .2f would be a float with the approximate value of .2. When you do integer division, things truncate. 5 goes into 1 0 times, so the result is correct. After the integer division, there is a cast up to double, but the result is still 0.

-Lee
 
parapup

parapup

macrumors 65816
Oct 31, 2006
1,291
49
Duke Leto said:
However, when I set the values to fractions, it is still 0!
Code: 
...
a[2][1] = 1/5;
...
But if I set them directly, it works!
Code: 
...
a[2][1] = .2;
...
Why don't these arrays work!
Click to expand...

1/5 - both 1 and 5 are treated as integers by the compiler. So you need a explicit type cast like the below or use 1.0/5.0.

Code: 
a[2][1] = (double)1/(double)5
 
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