Modify an array elements using a for loop

I am confused on for loops. I don't really udnerstand how a for loop works in this context. My professor or textbook were no help.

I

Answer 1

[Walter Roberson]

As an outline,

for index_variable = start_value : increment : final_value
    if some_array(index_variable) satisfies some condition
        calculate new value
        some_array(index_variable) = new value
    end
end

Answer 2

[VBBV]

numberSamples =  4;
userSamples = [2 12 9 20];
minValue = 10;

for k = 1:numberSamples
    if userSamples(k) < minValue
        userSamples(k) = 2*userSamples(k);
    end
end
userSamples

userSamples = 1×4

4 12 18 20

[VBBV]

% declare input variables 
numberSamples =  4;
userSamples = [2 12 9 20];
minValue = 10;

% call the function (preferably from command window (>>)
dataSamples = AdjustMinValue(numberSamples,userSamples,minValue)

dataSamples = 1×4

4 12 18 20

function dataSamples = AdjustMinValue(numberSamples,userSamples,minValue)
    dataSamples = userSamples;
    for k = 1:numberSamples
        if userSamples(k) < minValue
            userSamples(k) = 2*userSamples(k);
        end
    end
    % assign it desired variable name
    dataSamples = userSamples;
end

[Walter Roberson]

My professor or textbook were no help.

... which is to say that this is a homework question.