/*
 *@author James McKenzie
 *@lang C89 Based
 *@contact lunarised@outlook.com
 */
void setup() {
    pinMode(0, OUTPUT);
  pinMode(1, OUTPUT);
    pinMode(2, OUTPUT);
  pinMode(3, OUTPUT);
    pinMode(4, OUTPUT);
  pinMode(5, OUTPUT);
  pinMode(6, OUTPUT);
  pinMode(7, OUTPUT);
  pinMode (11, INPUT_PULLUP);
   pinMode (8, INPUT_PULLUP);
    pinMode (9, INPUT_PULLUP);
     pinMode (10, INPUT_PULLUP);
int  i = 0;
int j = 0;
int sum = 0;
  resetDisplay();
}
int i;
int j;
int sum;
int result;
int error;
void loop() {
  int error = 0;
  i = stateA(i);
  delay (250);
  j = stateA(j);
  delay(250);
  int operand = stateB();
   stateC(operand);
  delay(250);
  stateD();
  digitalWrite(1, LOW);
  delay(1000);
  digitalWrite(1, HIGH);  
}
int stateA(int val){
  while (digitalRead(11)==HIGH){
    if (digitalRead(8)==LOW){
      val = (val + 1)%10;
      displayDigit(val, 100);
    }
        if (digitalRead(9)==LOW){
      val = (val + 9)%10;
      displayDigit(val, 100);
    }
    displayDigit(val, 100);
  }
  return val;
}
int stateB(){
int operand = 0;
digitalWrite(1, LOW);
while (operand == 0){
  if (digitalRead(11) == LOW){
    operand = 1;
  }
    if (digitalRead(10) == LOW){
    operand = 2;
  }
    if (digitalRead(9) == LOW){
    operand = 3;
  }
    if (digitalRead(8) == LOW){
    operand = 4;
  }
}
digitalWrite(1, HIGH);
return operand;
}
void stateC(int operand){
if (operand == 1){
  sum = i + j;
}
if (operand == 2){
  sum = i - j;
}
if (operand == 3){
  sum = i * j;
}
if (operand == 4){
  if (j == 0){
    error = 1;
  }
  else{
    sum = i / j;
  }
}
}
void stateD(){
  if (error == 1){
          digitalWrite(0, LOW);
            digitalWrite(1, LOW);
            digitalWrite(2, LOW);
            digitalWrite(3, LOW);
            digitalWrite(4, LOW);
            delay (5000);
            error = 0;
  }
  else{
  while (digitalRead(11)==HIGH){
int   splitSum = sum;
    while(splitSum >= 9){
  displayDigit(splitSum%10, 250);
  splitSum /= 10;
    }
    displayDigit(splitSum, 250);
  }
  }
}
void displayDigit(int inp, int fTime){
    switch (inp){
      case 1:
      digitalWrite(5, LOW);
      digitalWrite(6, LOW);
      delay(fTime);
      resetDisplay();
      break;
      case 2:
      digitalWrite(0, LOW);
      digitalWrite(1, LOW);
      digitalWrite(2, LOW);
      digitalWrite(4, LOW);
      digitalWrite(5, LOW);
      delay(fTime);
      resetDisplay();
      break;
      case 3:
      digitalWrite(0, LOW);
            digitalWrite(1, LOW);
            digitalWrite(2, LOW);
            digitalWrite(5, LOW);
            digitalWrite(6, LOW);
      delay(fTime);
      resetDisplay();
      break;
      case 4:
      
            digitalWrite(1, LOW);
            digitalWrite(3, LOW);
            digitalWrite(5, LOW);
            digitalWrite(6, LOW);
            delay(fTime);
      resetDisplay();
      break;
      case 5:
            digitalWrite(1, LOW);
      digitalWrite(0, LOW);
      digitalWrite(2, LOW);
      digitalWrite(3, LOW);
      digitalWrite(6, LOW);
      delay(fTime);
      resetDisplay();
      break;
      case 6:
            digitalWrite(1, LOW);
      digitalWrite(0, LOW);
      digitalWrite(2, LOW);
      digitalWrite(4, LOW);
      digitalWrite(3, LOW);
      digitalWrite(6, LOW);
      delay(fTime);
      resetDisplay();
      break;
      case 7:
      digitalWrite(2, LOW);
      digitalWrite(5, LOW);
      digitalWrite(6, LOW);
      delay(fTime);
      resetDisplay();
      break;
      case 8:
      digitalWrite(2, LOW);
            digitalWrite(1, LOW);
      digitalWrite(0, LOW);
      digitalWrite(4, LOW);
      digitalWrite(3, LOW);
      digitalWrite(5, LOW);
      digitalWrite(6, LOW);
      delay(fTime);
      resetDisplay();
      break;
      case 9:
      digitalWrite(2, LOW);
            digitalWrite(1, LOW);
      digitalWrite(0, LOW);
      digitalWrite(3, LOW);
      digitalWrite(5, LOW);
      digitalWrite(6, LOW);
      delay(fTime);
      resetDisplay();
      break;
      case 0:
      digitalWrite(2, LOW);
      digitalWrite(0, LOW);
      digitalWrite(3, LOW);
      digitalWrite(4, LOW);
      digitalWrite(5, LOW);
      digitalWrite(6, LOW);
      delay(fTime);
      resetDisplay();
      break;      
    }
  };
void resetDisplay(){
  digitalWrite(0, HIGH);
  digitalWrite(1, HIGH);
  digitalWrite(2, HIGH);
  digitalWrite(3, HIGH);
  digitalWrite(4, HIGH);
  digitalWrite(5, HIGH);
  digitalWrite(6, HIGH);
  digitalWrite(7, HIGH);
}