write an integer to file using a function

[snippsat]

Use str(z) + "\n".
Here some fixes in your code,use 4-space indentation,a function should take argument,
and not getting the value for global namespace over.
Use r raw string in Path,you are using Python 2 as C:\Users will give SyntaxError in Python 3.

r"C:\Users\Kingsley\Projects\X\wite.csv"

Use Python 3,not Python 2 as is dead in under a month.

def joinFunction(z1, s):
    x = 5
    y = 6
    z = x + y
    z1.write(str(z) + "\n" + s)
    z1.close()

z1 = open("wite.csv", "w")
v = "python is "
x = "pretty awesome "
y = "and amazing"
s = v + x + y
joinFunction(z1, s)

Output:
11
python is pretty awesome and amazing

With f-string can just put in \n.

with open('out.txt', 'w') as f:
    x = 5
    y = 6
    z = x + y
    c = x ** y
    f.write(f'Result is {z}\nResult is {c}')

Output:
Result is 11
Result is 15625