Computing multiple numbers with multiple operations - arduino

Question

So I am creating a calculator that will compute numbers.I have this code(I will not include very basic codes)
long num1, num2, answer;
boolean mySwitch = false;
boolean do_subtraction_flag = false; // when true we will apply subtraction
boolean multiply = false;
boolean divide = false;
void loop()
{
char keypressed = myKeypad.getKey();
if(keypressed != NO_KEY)
{
Serial.print(keypressed);
if(keypressed > 47 && keypressed < 58) // is between '0' and '9'
{
if(!mySwitch)
{
num1 = (num1 * 10) + (keypressed - 48);
}
else
{
num2 = (num2 * 10) + (keypressed - 48);
}
}
if(keypressed == '=')
{
if(do_subtraction_flag) // we want to subtract the numbers
{
answer = num1 - num2;
}else if(multiply){
answer = num1 * num2;
}else if(divide){
answer = num1 / num2;
}
else // we want to add the numbers
{
answer = num1 + num2;
}
Serial.println(answer);
num1 = 0;
num2 = 0;
mySwitch = false;
do_subtraction_flag = false;
multiply = false;
divide = false;
}
else if(keypressed == '+')
{
mySwitch = true;
}
else if(keypressed == '*'){
mySwitch = true;
multiply = true;
}else if(keypressed == '/'){
mySwitch = true;
divide = true;
}
else if(keypressed == '-')
{
mySwitch = true;
do_subtraction_flag = true;
}else if (keypressed == 'C'){
for (int i=0; i < 80; i++)
{
Serial.write(8); // print 80 times backspace (BS)
}
}
}
}
Im confused here because I want to compute multiple number with multiple operands (eg., 2+1+3 or 2+1-2), but when i add another variable 'num3' what should I suppose to do with it? if i put it into the do_subtraction flag what if the user inputs 2-1+3?Is it possible to compute 3 numbers with this code?I'm getting confused here but let me know if you are also confused what I want to do

Answer 1

Make an array to hold the numbers and operators that you input, then loop through them when the input == '='. Have your num1 always hold the result and num2 hold the next array value.