How to Pass a Parameter Value to an IEnumerator?

Hello!

I am creating a game that calculates multiple status effects every interval. Because Update is too fast, and because I want to calculate any physics I add in game using FixedUpdate, which will surely use a different timestep than my calculations, I am using a coroutine for them. My problem is that, previously, the calculations could be modified by player input when a UI button was clicked. I did this by setting the button to directly feed a parameter as a string into my method that was at that point being called in FixedUpdate. The method would then execute a switch statement comparing the same string, and execute the appropriate case. At the end of each case, the string was reset so the default case would be run if no button was pressed in between calculation steps.

However, in converting the process to a coroutine, I still am able to run the default case at interval, but I've lost the ability to change the parameter in-game using the UI buttons. Whereas I could set such changes up in the OnClick() component in the inspector, the same option is no longer available to me. My question is, how do I pass a parameter from a UI button into an IEnumerator, or is there a different method/workaround?

Here is my current script:

 //variables for hunger
 int hunger = 200;
 int hunger_rate = -1;

 //variables for thirst
 int thirst = 200;
 int thirst_rate = -1;

 //variables for sleep
 int sleep = 200;
 int sleep_rate = -1;
 bool isAwake = true;

 //this variable controls which calculation runs, supposed to be controlled in-game by buttons
 string casetype = "default";

 int money = 1000;
 int interest_rate = 15;

 public Text debug;

 IEnumerator Start()
 {
     while(true)
     {
         StartCoroutine(Calculate(casetype));
         yield return new WaitForSeconds(1);
     }
 }

 IEnumerator Calculate(string casetype)
 {
     switch (casetype)
     {
         //if nothing is pressed, calculate
         case "default":
             //if the Squooshi is awake, it gets hungier and thirstier
             if (isAwake)
             {
                 hunger = hunger + hunger_rate;
                 thirst = thirst + thirst_rate;
             }
             //sleep equation is set up to be reverse compatible whether or not Squooshi is awake
             sleep = sleep + sleep_rate;
             //money don't sleep
             money = money + interest_rate;

             //reset varables at the end of calculation
             hunger_rate = -1;
             thirst_rate = -1;
             break;

         //buy a burger and feed it to the Squooshi
         case "feed":
             if (money - 100 > 0)
             {
                 hunger_rate = 200;
                 money = money - 100;
             }

             casetype = "default";
             break;

         //buy a water bottle and feed it to the Squooshi
         case "hydrate":
             if (money - 200 > 0)
             {
                 money = money - 200;
                 thirst_rate = 200;
             }

             casetype = "default";
             break;

         case "medicate":
             //toggle whether or not the Squooshi is sleeping
             if (money - 500 > 0)
             {
                 isAwake = !isAwake;
                 money = money - 500;
             }

             //if the Squooshi is awake, it gets more tired
             if (isAwake)
             {
                 sleep_rate = -1;
             }

             //if the Squooshi is sleeping, its tiredness is reduced
             if (!isAwake)
             {
                 sleep_rate = 3;
             }

             casetype = "default";
             break;
     }
     yield return null;
     debug.text =
         "Money: " + money.ToString() +
         " Hunger: " + hunger.ToString() +
         " Thirst: " + thirst.ToString() +
         " Sleep: " + sleep.ToString();
 } 

Would like to point out: -returning the casetype to "default" at the end of each case is redundant, done so to reduce chance of bugs during testing -I have no idea what "yield return null;" means or exactly what it's doing here--I just know I need a yield return for the IEnumerator not to yell at me

Thanks everyone, you are always so helpful! <3