Where is the 5 goes?

Question

printf("%08.3f", 17.3456);
/* output: 0017.346*/

Why the output is 0017.346 and not 0017.345?

And when i change it like this..
printf("%08.3f", 17.345);
/* output: 0017.345*/

The output now is what i'm expected...

Answer 1

Because the next decimal is greater than 5
e.g.
4.1234 = 4.123
4.1267 = 4.127

And same with that case, you round the number into 3 decimal places
--> 17.3456
--> 17.345(6) <-(6 is greater than or equal to 5)
--> 17.34(5+1) <-(if next decimal is greater than 5 add 1 to the decimal to its left.
== 17.346

Answer 2

Adding to what had been pointed out correctly early on, the number 17.3456 had 4 decimal points, but format specifier "%08.3f" allows only 3 decimal points, meaning, a rounding was in order.

Notice that by adding decimal point (to 4 points) in format speciifier we can get output as expected.

printf("%08.4f\n", 17.3456);
// 08.4f output 017.3456
// width 8 characters, pad with '0'
// where necessary, 4 decimal
// point allowed, type float

printf("%08.3f\n", 17.3456);
// 08.3f output: 0017.346
// width 8 characters, pad with '0'
// where necessary, 3 decimal
// point allowed, type float

P.S. The decimal separator '.' is also counted in width specifier.

Answer 3

Because of the ".3f" it rounding your number.