Greatest Common Divisor, Recursive code

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Kitt Naughton
Kitt Naughton 2020-2-22
编辑： Walter Roberson 2024-8-21
Hello,
This code uses recursion to find the GCD of two numbers that are inputed. The code works but for some reason GCD is being assigned to 0 at the end. The test case I am using sets greatestCommonDivisor(10007,500).
Any help is greatly appreciated
The code is as follows:
function GCD = greatestCommonDivisor(a, b)
if(a > b)
temp1 = a;
temp2 = b;
else
temp1 = b;
temp2 = a;
end
if temp1 == 0
GCD = temp2;
return
elseif temp2 == 0
GCD = temp1;
return
else
r = rem(temp1, temp2);
end
if(r == 0)
disp(temp2)
if(temp2 == 1)
GCD = 1;
disp(GCD)
return
else
GCD = temp2;
return
end
else
greatestCommonDivisor(temp2, r);
end
end
  1 个评论
Jalaj Gambhir
Jalaj Gambhir 2020-2-25
Hi,
I do not see where GCD is assigned to 0, can you provide more clarifications/ output screenshot or something? Works fine for me, with GCD = 1 at the end.

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回答（1 个）

Deepak
Deepak 2024-8-21
Hi @Kitt Naughton, To my understanding, you have written code to calculate GCD of two integers.
Your code works fine, but the GCD variable is being assigned to 0 at the end.
To resolve this issue, when calling the recursive method “greatestCommonDivisor(temp2, r)” at the end, you need to assign the return value to the output variable GCD.
GCD = greatestCommonDivisor(temp2, r);
It is important to assign the result of a recursive call to a variable so that the result can be returned up the call stack.
By assigning “GCD = greatestCommonDivisor(b, r)” you capture this result and ensure it is returned correctly.
Here is the updated MATLAB code:
function GCD = greatestCommonDivisor(a, b)
if(a > b)
temp1 = a;
temp2 = b;
else
temp1 = b;
temp2 = a;
end
if temp1 == 0
GCD = temp2;
return
elseif temp2 == 0
GCD = temp1;
return
else
r = rem(temp1, temp2);
end
if(r == 0)
disp(temp2)
if(temp2 == 1)
GCD = 1;
disp(GCD)
return
else
GCD = temp2;
return
end
else
GCD = greatestCommonDivisor(temp2, r);
disp(GCD);
end
end
I hope this helps.

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