I have a very good example of the program you need written on Python. You can use this (sorry for bad tabulation):
import math
import math
def main():
function = input("Enter a function f(x):\n")
x = 0
y = 0
for rows in range(10,-11,-1):
for col in range(-10,11,1):
x=col
roundfx = round(eval(function))
if roundfx == rows:
print("o", end="")
if rows==0 and col==0 and not rows == roundfx:
print("+", end="")
if col == 0 and not rows == 0 and not rows == roundfx:
print("|", end="")
if rows==0 and not col==0 and not rows == roundfx:
print("-", end="")
else:
if not rows == 0:
if not col == 0:
if not rows == roundfx:
print(" ", end="")
print()
main()
