You need to review your logic. What conditions are true when a button is pressed for the first time? And how do those conditions differ from what happens when the button is pressed a second time? You probably need to keep track of whether a timer is running. If you use code like I wrote below it is easier to change behavior and add or remove pins as needed.
Note that ==1 is only needed if pin_value can also have other non-zero values.
pins=struct;
pins(1).read='D2';
pins(1).write='D10';
pins(1).RunningTimer=false;
pins(1).tic_handle=[];
pins(2).read='D4';
pins(2).write='D13';
pins(2).RunningTimer=false;
pins(3).read='D6';
pins(3).write='D12';
pins(3).RunningTimer=false;
pins(4).read='D8';
pins(4).write='D11';
pins(4).RunningTimer=false;
a = arduino; %register Arduino Uno
while true %make code continuous
for n=1:numel(pins)
pin=pins(n);%store for shorter syntax
pin_value=readDigitalPin(a,pin.read);
if pin_value==1
%button pushed
if ~pin.RunningTimer % first time
%start timer
pin.tic_handle=tic;
pin.RunningTimer=true;
writeDigitalPin(a,pin.write,1);
else
%stop timer
pin.RunningTimer=false;
toc(pin.tic_handle)
writeDigitalPin(a,pin.write,0);
end
else
%button not pushed
end
pins(n)=pin;
end
end
