Vrftjkry

I am trying to sum up entries in a table and thought using the fp package was the way to go. The MWE below,

AddToTotal{18,000.00}

AddToTotal{-17,000.00}

AddToTotal{-8,000.00}

yields:

as expected. However, splitting the -8,000 into two steps breaks things:

AddToTotal{18,000.00}

AddToTotal{-17,000.00}

AddToTotal{-7,000.00}

AddToTotal{-1,000.00}% <--- Why this break things?

which should yield the same result instead produces the error:

FP error: UPN stack is empty!.
FP@errmessage #1->errmessage {FP error: #1!}

l.25 AddToTotal{-1,000.00}
% <--- Why this break things?

Should I be using a different package for this? I only need 2 digits of precision, so perhaps there are better options.

Code:

documentclass{article}

usepackage{xstring}

usepackage{siunitx}



usepackage{fp}



newcommand*{Total}{0.00}% Initial Value

newcommand*{AddToTotal}[1]{%

    StrDel{#1}{,}[NewAmount]%

    FPevalTempTotal{Total+NewAmount}%

    xdefTotal{TempTotal}%

    %% --------

    par

    After adding $NewAmount$, total is num[round-mode=places,round-precision=2]{Total}.%

}%



begin{document}

    AddToTotal{18,000.00}

    AddToTotal{-17,000.00}

    AddToTotal{-7,000.00}

    AddToTotal{-1,000.00}% <--- Why this break things?

end{document}

The problem can be easily fixed by adding extra parentheses in your AddToTotal command:

FPevalTempTotal{(Total)+NewAmount}%  <-- extra parentheses around Total

Without the parentheses, a negative Total is expanded as is, giving something like -6000+-1000 where the first expression is interpreted as a subtraction rather than a negative number. fp then produces an empty stack error because the second operand for that subtraction is missing on the internal stack.

To fix that you have to give it a hint that the negative number is a single atom by putting a pair of parentheses around it. You now correctly get:

That alternative version also seems to work:

FPevalTempTotal{0+Total+NewAmount}

Not sure why the parsing works differently at the start of the expression than in the middle.

Why not using expl3 directly? You load it anyway, because of siunitx.

documentclass{article}

usepackage{siunitx} % also loads xparse and expl3



sisetup{

  round-mode=places,

  round-precision=2,

  group-separator={,},

  group-four-digits,

}





ExplSyntaxOn



fp_new:N g_grill_total_fp % initialized to 0

tl_new:N l__grill_total_temp_tl



NewDocumentCommand{AddToTotal}{m}

 {

  tl_set:Nn l__grill_total_temp_tl { #1 }

  tl_remove_all:Nn l__grill_total_temp_tl { , }

  fp_gadd:Nn g_grill_total_fp { l__grill_total_temp_tl }

  After~adding~num{tl_use:N l__grill_total_temp_tl},~

  total~is~num{fp_use:N g_grill_total_fp}.

  par

 }

ExplSyntaxOff



begin{document}



AddToTotal{18,000.00}

AddToTotal{-17,000.00}

AddToTotal{-7,000.00}

AddToTotal{-1,000.00}



end{document}