How can I fix my while loop?
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Hi!
I am trying to create a program that reads a cell array and computes the answer ex:
t = {'mult','add','2','3','stop','add','4','5','stop','stop'} (So the equation is (2+3)*(4+5))
ans= 45.0000
here is my current code:
function [pos prod] = doMult ( expr, pos )
prod=1;
lm=length(expr)
expo=1;
sub=1;
quot=1;
sum=1;
while ~strcmp(expr{pos}, 'stop')
pos=pos+1
if strcmp(expr{pos}, 'pow')
[pos expo]=doPow(expr, pos)
elseif strcmp(expr{pos},'mult')
[pos prod]=doMult(expr, pos)
elseif strcmp(expr{pos}, 'div')
[pos quot]=doDiv(expr, pos)
elseif strcmp(expr{pos},'add')
[pos sum]=doAdd(expr, pos)
elseif strcmp(expr{pos},'sub')
[pos diff]=doSub(expr, pos)
else
ExprNUM=str2double(expr) %double type
prod=prod* ExprNUM(1,pos)*sum*diff*quot*expo
pos=pos
end
end
end
and the other finctions for doAdd and such would contain some variation of this . the output gives me an answer of 5, which is not correct. After going through what it calculates here:
lm =
10
pos =
2
lm =
10
pos =
3
ExprNUM =
NaN NaN 2 3 NaN NaN 4 5 NaN NaN
sum =
2
pos =
3
pos =
4
ExprNUM =
NaN NaN 2 3 NaN NaN 4 5 NaN NaN
sum =
5
pos =
4
pos =
5
ExprNUM =
NaN NaN 2 3 NaN NaN 4 5 NaN NaN
sum =
NaN
pos =
5
pos =
5
sum =
NaN
answer =
5
ans =
5
and it looks like it is not recognizing the stop and the function following it. How can I fix this?
Thanks!
1 个评论
Geoff Hayes
2019-2-21
Ashley - maybe you need to start with a simpler example and/or post more of your code. Is doMult the calling function or do you have some other function that you call first?
Note that if I try something simple like
g = {'mult' '2' '3' 'stop' }
doMult(g,1)
then I get an error
Undefined function or variable "diff".
Error in doMult (line 25)
prod=prod* ExprNUM(1,pos)*sum*diff*quot*expo
which makes sense because neither sum nor diff have been defined.
NOTE that sum and diff are built-in MATLAB functions so you should not be creating variables with the same names as these functions.
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2019-2-21
2019-2-21
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