Add not defined

Question

num1 =int(input("Enter number 1 /n"))
num2 = int(input("Enter number 2"))
op = input("Enter operation (add ,sub , mul , div")
x = num1 + num2
y= num1 - num2
z = num1 * num2
k = num1 / num2
if op == add:
print(x)
elif op == (sub):
print(y)
elif op == (mul):
print (z)
elif op == (div):
print(k)
else:
print("Error")
....i tried this using the double quotes too

Answer 1

"""
You get string from user input, so you need to compare value with string:
"""
# this 3 first line have some mistakes non blocking (display)...
num1 =int(input("Enter number 1 /n"))
num2 = int(input("Enter number 2"))
op = input("Enter operation (add ,sub , mul , div")
x = num1 + num2
y= num1 - num2
z = num1 * num2
k = num1 / num2
if op == "add":
print(x)
elif op == "sub":
print(y)
elif op == "mul":
print (z)
elif op == "div":
print(k)
else:
print("Error")