tcl expr not rounding like i expect

Question

Im new to tcl and i have these numbers:

set a 565056236086 set b 488193341805

the output of $a / $b is 1,157443552992375

When i use the following code

set num [expr {double(round(100*$a / $b))/100}]

the output is: 1,15

but i want 1.16 how can i round it like that?

Are you going to be doing further calculations with the value, or is this for display? — Donal Fellows, Jul 22 '19 at 10:41

score 2 · Accepted Answer · answered Jul 22 '19 at 10:08

You need to make either a or b a double before doing the operations. Also, round returns an integer, so you either need to convert it to double too, or divide by a double:

set num [expr {round(100*double($a) / $b)/100.0}]
# 1.16

Or if you specifically need to round up, then, you can use ceil (since this one returns a double, you don't need to divide by a double):

set num [expr {ceil(100*double($a) / $b)/100}]
# 1.16

score 0 · Answer 2 · answered Jul 22 '19 at 10:27

You will need to make sure you are doing floating point division by making sure either, or both values are a double (e.g. using double($a) and/or double($b)). Then rounding to a certain number of decimal digits is most easily done with format:

format %.2f [expr {double($a) / $b}]

tcl expr not rounding like i expect

2 Answers2