array of numbers and strings

Hi, I have an issue creating string. let say I have 2 numbers and a string:

nb1 = 12;
nb2 = 1;
str1 = '+';

I want to create a variable (array or a string) from these 3 variables:

op = {nb1 str1 nb2} ;

op is an operation, (i will later need to acces nb2 as a number value and fprint the whole op.)

I then need to make an array of op. This array is storing every operations made.

history = [];
for i = 1 : 5
    history = [history op];   %adding the last operation in the history
    nb1 = nb1 + i;            %just changing the numbers in a random way to illustrate
    nb2 = nb2 - i;

str1 will also change for an other string, I lack imagination to illustrate that...

op = {nb1 str1 nb2};
end

i want to be able to access a certain operation in the history and fprintf it on the screen.

op = history (n*2);
fprintf ('%s',op);

And finally, also change the value of a number from the previous value.

nb1 = op{1};

op and nb1 at this stage should be what they were "n" operation before.

Answer 1

[Geoff Hayes]

Marc-Olivier - the line of code

 op = {nb1 str1 nb2} ;

will create a 1x3 cell array of two numbers (in the first and third positions) and a string (for the operation). It is not a string.

If you have several operations/equations, then you can concatenate them together to form the history as

 history = [];
 for k=1:5
     numA = randi(255,1,1);
     numB = randi(255,1,1);
     operator = '+';
     eqn = {numA operator numB};
     history = [history ; eqn]; % vertical concatenation using ;
 end

If you wish to access the third equation in the history, you would then do

 thirdEquation = history(3,:);

You are accessing the third row (so use 3) and you want all of the columns (so use the colon).

To print this equation, you would do

 fprintf('%d %s %d\n', thirdEquation{1}, thirdEquation{2}, thirdEquation{3});

where you specify the type of each element in your equation: number, string, number.

You should then be able to manipulate any of the values in this third equation via the usual manner of accessing elements in the cell array.

[Marc-Olivier Labrecque-Goulet]

thanks a lot Geoff, im going to try this right away.

[Marc-Olivier Labrecque-Goulet]

update : everything work fine, ive finally finish the function Undo of my "very basic" calculator Ty very much