Help with accessing variables outside a function

I am trying to create a function with two inputs: input_data(a,b). The input 'a' will indicate the sampling rate and input 'b' indicates the value. So if it was input_data(30,400), the data will be written to a text file with the value 400 from indexes 1-30. As an example:

1   400
2   400
3   400
4   400
.   400
.   400
.   400

How do i make the function so that everytime i call the function, it appends to the previous list in the text file? I want it to continue incrementing the index values from the previous entry. Thank you.

Answer 1

[Bandar]

This is my code for your question

function [] = input_data(a, b)

file = fopen('data.txt', 'a+'); % append data to an existing txt file (Note: 'a' for appending)

A = textread('data.txt');

if (isempty(A))
    i = 1;
    for i = i:1:a
        fprintf( file, '%i  %f ', i, b);
        i = i + 1;
    end
else
    start = A( size(A,2) - 2) + 1;
    for j = start:1:a+start-1
        fprintf( file, ' %i  %f ', j, b);
    j = j + 1;
    end   

end    

fclose(file); 
end

in the main,

>> input_data(2, 400)
>> input_data(2, 400)
>> input_data(3, 300)

In the txt file

1  400.000000 2  400.000000  3  400.000000  4  400.000000  5  300.000000  6  300.000000  7  300.000000

Hope this helps.

[Victor]

If i call the function again with a different a and b value, will the index continue incrementing from the previous value in the text file?

[Bandar]

@Victor, I've updated the code. The answer for your comment is Yes. Mark it as solved if you think this works for you.

[Victor]

matlab is telling me to use textscan instead of textread. how do i implement this?

[Victor]

also, if i were to use more than 2 inputs lets say: input_data(a, b, c, d, e). Then the code does not work. 'a' would still indicate the index and 'b', 'c', 'd', 'e' would represent inputted constant values like "400."

[Bandar]

I suggest you to make another question that suits your needs. The answer is for your first question.