# Convert for loop to while loop

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Kathleen Whitmore on 5 Oct 2020
Edited: madhan ravi on 5 Oct 2020
Hi!
I am trying to convert a for loop to a while loop that will produce the same result. Although I understand the concept, I keep running into an error that I'm not sure how to fix. Any help would be appreciated!
The for loop:
x=0;
y=randi(100,1,5);
for i = 1:5 x=x+y(i);
end disp(x);
And I came up with the while loop:
x=0;
y=randi(100,1,5);
i=1;
while i <= 5
i=i+1;
x=x+y(i);
end
disp(x);
However, it keeps giving me the error "Index exceeds the number of array elements (5).
Error in Example (line 6)
x=x+y(i);"
I don't understand why this is happening, since the while loop should run 5 times, increasing the i value by 1 each time, and the vector y has 5 elements.
Like I said, any help would be appreciated! Thank you!

madhan ravi on 5 Oct 2020
Edited: madhan ravi on 5 Oct 2020
Initialise ii with 0 instead of 1. Otherwise you start it as 2 therefore when you reach 5 it gets incremented to 6 exceeding the number of elements in y which has 5 elements.

#### 1 Comment

madhan ravi on 5 Oct 2020
y = randi(100, 1, 5);
x = zeros(size(y)); % preallocate x properly
ii = 0;
while ii <= 5
ii = ii + 1;
x(ii) = x(ii) + y(ii);
end
x