Interesting output using variables with NSLog() in objective-c

Question

The following code:

int N = 100;
double total_time = 100;
double dt = total_time/N;
NSLog(@"Answer: %d", dt);

gives an interesting output: 5766 instead of 1.

Only in the case of adding

NSLog(@"Answer: %f", dt);

outputs the right answer. However, I would like to output "double" value instead of "float". What's wrong with my expectations and syntax?

You should already know basic C if you are attempting Objective-C, and one of the things you should know is the simple `printf` format scheme (as well as the difference between an integer and a float value). — Hot Licks, Apr 07 '15 at 18:49
Do you mean that I shouldn't ask the questions about Objective-C if I do not know basic C so good? How do you define what is basic and what is not? For me, some questions look basic, for others - not. — Darius Miliauskas, Apr 07 '15 at 18:55
If you don't know, eg, how to use `printf` to print floating point values, that's a good sign that you're not familiar enough with C to be starting into Objective-C. — Hot Licks, Apr 07 '15 at 18:58

score 1 · Accepted Answer · answered Apr 07 '15 at 18:27

1

%d means "decimal representation of int", not "double".

You always output a double value using %f, because NSLog() has an open arg list. In such a case, all floating point numbers are passed as doubles. So you should read %f as "floating point number" not float.

answered Apr 07 '15 at 18:27

Amin Negm-Awad

16,582
3
35
50

Now, I see. But why the value of "5766"is chosen? – Darius Miliauskas Apr 07 '15 at 18:30
1

The "5766" isn't an arbitrarily chosen value, but rather its what the bytes represent when interpreted as a signed 32bit integer which is what %d is specified to do. – illeyezur Apr 07 '15 at 18:51

score 1 · Answer 2 · answered Apr 07 '15 at 18:27

1

%d and %i are the same thing, both decimal integer formats.

answered Apr 07 '15 at 18:27

Phillip Mills

30,888
4
42
57

Interesting output using variables with NSLog() in objective-c

2 Answers2