Arduino Calculator (Multiple Button Pressing) - arduino

Question

We're currently making a 4x3 calculator using Arduino and LCD. We're lacking buttons so instead of one button per operation, there's only one button for all operations. So far, it only does addition. How do you do the thing wherein if I pressed the OPERATION button once, it does addition, if twice, subtraction, etc.
#include <Keypad.h>
#include <LiquidCrystal.h> //import lcd library
LiquidCrystal lcd(12, 11, 5, 4, 3, 2); //lcd pins
//LiquidCrystal lcd(5,4,3,2,1,0);
const byte ROWS = 4; // four rows
const byte COLS = 3;
//define the keymap
char keys [ROWS] [COLS] = {
{'1', '2', '3'},
{'4', '5', '6'},
{'7', '8', '9'},
{'+', '0', '='}
};
byte rowPins[ROWS] = {
9 ,8 ,7 ,6}; //connect keypad ROW1, ROW2, ROW3, ROW4 to these arduino pins
byte colPins[COLS] = {
13, 10, 1};
//create the keypad
Keypad myKeypad = Keypad( makeKeymap(keys), rowPins, colPins, ROWS, COLS );
//variables declaration
boolean valOnePresent = false;
boolean next = false;
boolean final = false;
String num1, num2;
int ans;
char op;
void setup(){
lcd.begin(16,2);
lcd.setCursor(2,0);
lcd.print("Calculator");
delay(2500);
lcd.clear(); //clears the LCD screen and positions the cursor in the upper-left corner.
}
void loop(){
char key = myKeypad.getKey();
if (key != NO_KEY && (key=='1'||key=='2'||key=='3'||key=='4'||key=='5'||key=='6'||key=='7'||key=='8'||key=='9'||key=='0')){
if (valOnePresent != true){
num1 = num1 + key;
int numLength = num1.length();
lcd.setCursor(15 - numLength, 0); //to adjust one whitespace for operator
lcd.print(num1);
}
else {
num2 = num2 + key;
int numLength = num2.length();
lcd.setCursor(15 - numLength, 1);
lcd.print(num2);
final = true;
}
}
else if (valOnePresent == false && key != NO_KEY && (key == '/' || key == '*' || key == '-' || key == '+')){
if (valOnePresent == false){
valOnePresent = true;
op = key;
lcd.setCursor(15,0);
lcd.print(op);
}
}
else if (final == true && key != NO_KEY && key == '='){
if (op == '+')
{
ans = num1.toInt() + num2.toInt();
}
else if (op == '='){
ans = num1.toInt() + num2.toInt();
}
/* else if (op == '+')
{
answ = num1.toInt() - num2.toInt();
}
*/
lcd.clear();
lcd.setCursor(15,0);
lcd.autoscroll();
lcd.print(ans);
lcd.noAutoscroll();
}
}

Answer 1

You could use an array in order to accomplish this. By implementing a while loop with a small delay you can keep iterating through the positions in the array every time the button is pushed until the array times out. Here's an example of some could you could use to implement it.
char ops [4] = {'+','-','/','*'};
int del = 2500;
int strt = millis();
int location = 0;
while (millis() - strt < del) {
key = myKeypad.getkey();
if (key == '+') {
if (loc == 3) {
location = 0;
}
else {
location += 1;
}
strt = millis();
}
}
op = ops(location);