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how to use conditional statement realizing prime function

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Shuoze Xu
Shuoze Xu 2022-6-17
评论： Walter Roberson 2022-6-19
Hi.
I want to use code to check if a number isprime. I know isprime () but I don't want to use it because I want to know how to use judgments to do tha.
Here is my code.
%function code
function[a,b] = isPrime(n)
% A number, n, is not prime if any number between 2 and n/2 divides the number without any remainder.
a = 1; % a = 1 means true
b = 0; % b = 0 means false
half = n/2; % get the half nums of n
for i = 2:half
if(mod(n,i)~=0) % if there is remainder
continue; % keep check
elseif(mod(n,i) == 0)
disp(b); % display false
break; % stop loop
end
disp(a);
end
end
% driver code
n = 9;
[x1,x2]= isPrime(n);
disp(isPrime(n));
Sample test:
isPrimedriver
0
0
1
It should output zero and stop looping, why it work twice?
And how to modify my code?
Thank you.
  4 个评论
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Walter Roberson
Walter Roberson 2022-6-18
编辑：Walter Roberson 2022-6-18
there are exceptions:
  • mod(inf,i) is nan
  • mod(nan,i) is nan
  • problems if n is empty or not a scalar

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采纳的回答

Voss
Voss 2022-6-18
Ran in:
Your driver code is calling isPrime two times.
% driver code
n = 9;
The first time, you only get a disp(b) from inside isPrime
[x1,x2]= isPrime(n);
0
The second time, you get a disp(b) from inside isPrime and then, after isPrime is done, you also disp the returned value from isPrime, which is a
disp(isPrime(n));
0 1
%function code
function[a,b] = isPrime(n)
% A number, n, is not prime if any number between 2 and n/2 divides the number without any remainder.
a = 1; % a = 1 means true
b = 0; % b = 0 means false
half = n/2; % get the half nums of n
for i = 2:half
if(mod(n,i)~=0) % if there is remainder
continue; % keep check
elseif(mod(n,i) == 0)
disp(b); % display false
break; % stop loop
end
disp(a);
end
end

更多回答（1 个）

Walter Roberson
Walter Roberson 2022-6-17
Hint:
prime_detected = true
for appropriate things
if appropriate condition
prime_detected = false;
break;
end
end

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