fprintf- I dont want to print one result.

Question

Gyp 2019-12-15

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/496723-fprintf-i-dont-want-to-print-one-result

编辑： dpb 2019-12-15

This is my code. I want that when the person put the value 0, the message print ONLY "Negative,has not being infected". But instance it give also the hour of being infected.

x= input ('Enter x:  '); %Degree of reaction to the virus from a blood test.
if x==0
    disp ('Negative, has not being infected.')
   N=0;
elseif  x<=11
    N= 3*x + 36;
elseif x > 11 && x<=33
    N= x*x - 10;
elseif x > 33 && x<=64 
    N= x-6;   
end
fprintf('\n%g hours of being infected.\n',N)

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Answer 1

Jesus Sanchez 2019-12-15

1
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https://ww2.mathworks.cn/matlabcentral/answers/496723-fprintf-i-dont-want-to-print-one-result#answer_406432

在 MATLAB Online 中打开

clear
clc
x= input ('Enter x:  '); %Degree of reaction to the virus from a blood test.
showHours = 1;
if x==0
    disp ('Negative, has not being infected.')
   N=0;
   showHours = 0;
elseif  x<=11
    N= 3*x + 36;
    
elseif x > 11 && x<=33
    N= x*x - 10;
    
elseif x > 33 && x<=64 
    N= x-6;   
end
if showHours
    fprintf('\n%g hours of being infected.\n',N)
end

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dpb 2019-12-15

编辑：dpb 2019-12-15

IF doesn't "give" a result, it just performs the test of the expression. x is a variable in the above code no different than the one you created and its value is the value of the expression to be tested.

See the definition of logical TRUE in MATLAB syntax at the documentation for if that says

"if expression, statements, end evaluates an expression, and executes a group of statements when the expression is true. An expression is true when its result is nonempty and contains only nonzero elements (logical or real numeric)."

Logical variables of T/F are 1/0, that is true, but the actual definition of true for logical tests is ~0/0. The idiom of if x==1 or if x==0 is completely superfluous in writing the explicit test.

Also note as it trips up most newbies is the phrase "and contains only nonzero elements". When testing array-valued expressions, all or any is needed to convert to a single logical result. You'll find many questions here on Answers that begin with "my expression fails to be true" owing to that oversight.

For one-liners like this my personal preference is the one-line expression rather than the full-blown indented construct. Don't let the formatting confuse you that there's anything different syntactically, though.

Jesus Sanchez 2019-12-15

wow, thanks for the detailed explanation!

dpb 2019-12-15

编辑：dpb 2019-12-15

在 MATLAB Online 中打开

Another way to recast...

x= input ('Enter x:  '); %Degree of reaction to the virus from a blood test.
if x<=0
  disp ('Test negative, subject has not been infected.')
  N=0;
  return
end
% set polynomial coefficeints by regime
if     x<=11,        b=[0 3  36]; end      % 3t+36
elseif x>11 & x<=33, b=[1 0 -10]; end      % t^2-10
elseif x>33 & x<=64, b=[0 1  -6]; end      % t-6
else   error("Reaction >64 beyond correlation range"), end
N=polyval(b,x);   % evaluate poly for x
fprintf('\nSubject %g hours of being infected.\n',N)