how can i declare a variable in a function for the first time only ,

2020 9 23
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更新时间：2020 9 23
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function h=src(input) %example
output=0 %here i won't output to be declared again when matlab gonna calcul src(input-1)
if input==0
output=output
else
output= output +1
src(input-1)
end

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Adam Danz
Adam Danz 2020-9-23
编辑：Adam Danz 2020-9-23

1 个投票

I think this is what you're looking for,
function h=src(input)
persistent output %%%%%%%%
if isempty(output) %%
output = 0; %%
end %%%%%%%%
if input==0
%output=output; % What's this ??
% Do nothing
else
output= output + 1;
src(input-1);
end
h = output; % assign output!
However, this still has problems.
  1. What if user enters src(-1)? What about src(.9)? The input will never reach 0 and you'll run out of memory. To prevent the user from entering negative or non-scalar values, use an argument validation function.
  2. You probably want to reset output back to 0 after input reaches 0. In that case, you can make this change,
if input==0
%output=output; % What's this ??
h = output;
output = 0;
else ...

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sofiane benhamza
sofiane benhamza 2020-9-23
编辑：Adam Danz 2020-9-23
it wasn't important to me , i'd just wrote it ,i thank you very mush but this code is my problem
it should computes the sum of digits of a positive number which is already given (ex: 12345=>1+2+3+4+5=15) , and it must containt recursive function, and i shouldn't worry about the input , but i couldn't understand , why it didn't
function h=src(input) %input is already given
h=0;output=0; %needed for calculations
if input == 0 % 0 gonna give 0
Output=output ;
s(Output) %to display the Output in screen , 3rd function
return
else
f(input) % to the second function
end
end
function z=f(input)
z=input*.1 %{ i'm trying to do it by this way ,
if input=214 , > z=214*.1=21.4 , a=(z-fix(z))*10=(21.4-21)*10 = 4
t=0; t will contain the final result t=t+a this works if z~=fix(x) (case when
a=0 , that's why i add if
if z==fix(z)
t=t+z;
else
a=(z-fix(z))*10;
t=t+a; %t should contain the final result
Output=t;
input=fix(z);
src(input) %return to the main function i there is more numbre 21 will be 2.1 and like this
t=t+1 ............;;t=t+2
end
end
function ss=s(k) %this one is just to display the result if found , but mt code still have problems and i
can't find them
ss=0;
display(k)
end
Adam Danz
Adam Danz 2020-9-23
So the input is 12345 or is it [1,2,3,4,5]?
sofiane benhamza
sofiane benhamza 2020-9-23
编辑：sofiane benhamza 2020-9-23
they said that it's one positive number , and i'm not allowed to use loops or str2num , i wish that it was a vector
Adam Danz
Adam Danz 2020-9-23
编辑：Adam Danz 2020-9-23
There are already lots of solutions for this within this forum.
Search the forum for phrases like
  • Convert integer to vector
  • Convert scalar to vector
  • 123 to 1 2 3
etc...

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