"""
Concatenate Stings.
"""
# Write your package code he
function cat_str end

"""
    cat_str(a, b)
Cat two string.
"""
function cat_str(a, b)
    string(a, b)
end

"""
    cat_str(a, b, c)
Cat three string.
"""
function cat_str(a, b, c)
    string(a, b, c)
end