if-statements for reassigning values

Question

Spaceman 2024-3-22

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https://ww2.mathworks.cn/matlabcentral/answers/2097786-if-statements-for-reassigning-values

评论： Spaceman 2024-4-8，3:26

Given: Write a script that creates a random integer N, which is in the range [-100,100]. If that number is in the range [-20,20], reassign N to be the current value of N multiplied by 2. If the number is greater than 20, reassign N to be the square root of the current value. Otherwise, reassign N to be the current value divided by 4.

Find: Use an if-statement to complete this.

Issue: I'm getting errors stating I don't know how to use '='. To me, my solution makes sense. But I have trouble with syntax in MATLAB.

My Solution:

N=randi([-100,100]);
if N=[-20,20]
    N=N*2
else if N>20
        N=sqrt(N)
else 
    N=N/4
end

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Answer 1

Voss 2024-3-22

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Use

if N >= -20 && N <= 20

And remove the space in "else if".

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Voss 2024-4-8，3:09

You're welcome!

Spaceman 2024-4-8，3:26

You're a real one!

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Answer 2

Steven Lord 2024-3-22

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Let's look at the exact text of the error you received.

N=randi([-100,100]);
if N=[-20,20]
Incorrect use of '=' operator. Assign a value to a variable using '=' and compare values for equality using '=='.
    N=N*2
else if N>20
        N=sqrt(N)
else 
    N=N/4
end

Using "N = [-20 20]" attempts to assign a vector with two elements to N. Assignment is not allowed in the condition part of an if statement.

Using "N == [-20 20]" (assuming N is compatibly sized) compares elements of N with elements of the vector [-20 20]. Comparison is allowed in the condition part of an if statement.

But you don't want to check if the elements in N are equal to -20 and 20. You want to check if they're in that interval. For that use the four inequality relational operators like < and >=. The and, & and or, | operators will also be of use.

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Spaceman 2024-3-22

Genius. This makes complete sense I forget I am generally only using logical operators with if and elseif statements. Also as Voss pointed out, I had a space in my elseif. Thank you for clearing that up.

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