How can I execute a function when key is pressed in Lua?

Question

I just want to execute findSum() function when '+' key is pressed. so when I press '+' key, then the function findSum() must be called. This is my program so far:

numberOfInput = 0                                               
sum = 0                                                         


io.write('\t', "Welcome to My Calculator", '\n')
repeat
io.write("for addition, press '+' :", '\n')
findSumSection = io.read()
until
(string.match(findSumSection, '+'))

function findSum()                              
io.write("Enter the amount of feed(s):",'\n')                   
numberOfInput = io.read()
x = numberOfInput                                               
for i = 1, x, 1 do                                                  
io.write('\n',"enter the number: ")
inputs = io.read()                                              
sum = sum + inputs                                              
end
return sum
end

io.write('\n',"The Sum of your feeds is:", '\n' , findSum(), '\n')  

io.write("Do you want to continue? [Y/N]")  
inputYesorNo = io.read()  


if (string.match(inputYesorNo, 'yes')) then
    print("Starting the program again")
    
else if(string.match(inputYesorNo, 'no')) then
os.exit()                                               
else
print("The program can not understand the procedure")       
end
end

Answer 1

Mike67 Thank you for testing the program. I think I fixed the problem. what I wanted to do was when I pressed the '+' key I wanted to go to the function findSum() to make it execute. I approached the problem in another program. take a look

function printMyName()
name = io.read()
return name
end

function findYourAge()
io.write("enter the current year:")
currentYear = io.read()
io.write('\n',"enter the year you were born:")
bornYear = io.read()
age = currentYear - bornYear
updatedAge = math.abs(age)
return updatedAge
end

function ageLimitToVote()
ageLimit = 18
newAgeForVote = 0
if(updatedAge < ageLimit) then
repeat 
updatedAge = updatedAge + 1
until 
updatedAge == ageLimit
newAgeForVote = updatedAge
return newAgeForVote
end
end

io.write("What is your name ", '\n')
io.write("your name is ", printMyName(), '\n')

io.write("Do you want to find your age?", '\n')
answer = io.read()
if(string.match(answer, 'yes')) then
findYourAge()
elseif(string.match(answer, 'no')) then 
os.exit()
end

if(updatedAge > 16) then
io.write(name, " you are matured enough to vote", '\n')
else
io.write(name, " you are ", updatedAge, " years old. and you have to wait until                you are ", ageLimitToVote(), '\n')
end

*here is the solution I implemented as I think, as best so far.

if(string.match(answer, 'yes')) then
findYourAge()