# Strange behaviour with if-else-Statements
**URL:** https://discourse.julialang.org/t/strange-behaviour-with-if-else-statements/47266
**Category:** Optimization (Mathematical)
**Tags:** jump, bug
**Created:** [September 25, 2020, 2:40pm UTC](https://discourse.julialang.org/t/strange-behaviour-with-if-else-statements/47266 "2020-09-25T14:40:08Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@SonntagK](https://discourse.julialang.org/u/SonntagK)
#### Post date: [September 25, 2020, 2:40pm UTC](https://discourse.julialang.org/t/strange-behaviour-with-if-else-statements/47266/1 "2020-09-25T14:40:08Z")
Hello,
I’m new to Julia and working with Julia/JuMP for optimization purposes. I want to use if-else-statements in the constraints I’m defining to write them more compact. When trying so I ran in some strange behaviour.
Im using `Julia v1.5.1` and `JuMP v0.21.3.`
1.) Just `Julia`: Writing the following into a .jl and running with include()
```julia
if 1 == 2
1
end
+ 5
```
returns the correct value `5` .
But writing the following into a .jl and running with include() gives an error.
```julia
if 1 == 2 1 end + 5
```
The Error is: `ERROR: LoadError: MethodError: no method matching +(::Nothing, ::Int64)`
2.) Using `Julia` and `JuMP`: When defining the following function ` Test()` the resulting constraint `con` in the .lp file is not like you would expect it
```julia
using JuMP
m = Model()
function Test(m::Model,set_constr::Int64)
@variable(m, x[1:5]>=0)
@constraint(m,con,
if set_constr == 1
x[1]
else
if set_constr == 2
0.1*x[2]
end
+
x[4]
+
if set_constr == 3
x[5]
else 0 end
end
<= 0)
JuMP.write_to_file(m, "model.lp")
empty!(m)
end
```
For ` Test(m,1)` we get: `con: 1 x_1_ <= 0` like we want to have.
For ` Test(m,2)` we get: `con: <= 0` while we would like to get `con: 0.1 x_2_ + x_4_ <= 0`
For ` Test(m,3)` we get `con: 1 x_5_ <= 0` while we would like to get `con: x_4_ + x_5_ <= 0 `
Is my understanding of the if-else-statement false here or is this a bug?
Thanks for your help and kind regards
Konstantin
---
### Author:  [@tomerarnon](https://discourse.julialang.org/u/tomerarnon)
#### Post date: [September 25, 2020, 2:57pm UTC](https://discourse.julialang.org/t/strange-behaviour-with-if-else-statements/47266/2 "2020-09-25T14:57:42Z")
This is not a bug. Starting a line with + doesn’t connect it with the previous line.
```julia
julia> 5
5
julia> +5
5
julia> 5 + 5
10
```
This is what’s happening
```julia
julia> if true
10
end + 5
15
julia> if false
10
end + 5
ERROR: MethodError: no method matching +(::Nothing, ::Int64)
```
You’re hitting the else case (i.e. your condition is false) which returns nothing. Nothing + Int is an error. The reason putting +5 on a new line works is because it’s parsed as
```julia
nothing # this line does nothing
+5 # +5 === 5, coincidentally this is what you wanted, but not for the right reason
```
You can use ternary expressions for compact if statements
```julia
x = 1 == 2 ? 15 : 10
```
Or you can use the boolean to do something directly if that makes sense in context
```julia
x = 10 + 5 * (1 == 2)
```
---
### Author:  [@Mason](https://discourse.julialang.org/u/Mason)
#### Post date: [September 25, 2020, 3:06pm UTC](https://discourse.julialang.org/t/strange-behaviour-with-if-else-statements/47266/3 "2020-09-25T15:06:38Z")
By the way, if for some reason you really want to write it that way, you can always just stick in a semi-colon to act as a newline:
```julia
julia> if false
10
end; + 5
5
```
---
### Author:  [@GerhardTotschnig](https://discourse.julialang.org/u/GerhardTotschnig)
#### Post date: [September 25, 2020, 3:40pm UTC](https://discourse.julialang.org/t/strange-behaviour-with-if-else-statements/47266/4 "2020-09-25T15:40:12Z")
It seems, as tomerarnon mentioned, a + in the beginning of a line in Julia does not represent a continuation of the line before. See:
> [@Best practice for avoiding line break bugs in long expressions](https://discourse.julialang.org/t/best-practice-for-avoiding-line-break-bugs-in-long-expressions/7475):
>
> I had a very frustrating debugging session yesterday. My code was running without errors but producing incorrect results. It took at least two hours for me to find this problem: x = a + really \* long + + (and + complex) / expression + - that \* (spans - several) + lines \* of / code Can you spot the error? The problem is that the expression terminates after the third line because I forgot to hang a trailing + sign there. The fourth line evaluates without error but doesn’t do anything…
Parentheses (or + at the end of the line) allows Julia to recognize the multiline code.
---
### Author:  [@SonntagK](https://discourse.julialang.org/u/SonntagK)
#### Post date: [September 25, 2020, 3:47pm UTC](https://discourse.julialang.org/t/strange-behaviour-with-if-else-statements/47266/5 "2020-09-25T15:47:24Z")
Thank you very much for your reply and the explanation! I see the problem with what I wrote.