Ruby solution

def letterconv(letter)
    larr = ["A","B","C","D","E","F","G","H","I","J","K","L","M","N","O","P","Q","R","S","T","U","V","W","X","Y","Z"]
    narr = [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26]
    i = 0
    while i < larr.length
        if letter == larr[i]
            return narr[i]
        end
        i += 1
    end
end

def gen_key_string(key,istr)
    istr = istr.gsub(" ",'')
    key = key.gsub(" ",'')
    istr = istr.upcase
    key = key.upcase
    karr = key.split(//)
    nkarr = []
    p = 0
    while nkarr.length < istr.length
        p = 0
        while p < karr.length
            if nkarr.length == istr.length
                break
            else
                nkarr << karr[p]
                p += 1
            end
        end
    end
    return nkarr
end

def strconv(strarr)
    narr = []
    i = 0
    while i < strarr.length
        narr << letterconv(strarr[i])
        i += 1
    end
    return narr
end

def stradd(strarr1,strarr2)
    i = 0
    narr = []
    while i < strarr1.length
        narr << strarr1[i] + strarr2[i]
        i += 1
    end
    return narr
end

def strshort(strarr)
    i = 0
    narr = []
    while i < strarr.length
        bit = strarr[i]
        if bit > 26
            bit = bit - 26
            narr << bit
        else
            narr << bit
        end
        i += 1
    end
    return narr
end

def numconv(num)
    larr = ["A","B","C","D","E","F","G","H","I","J","K","L","M","N","O","P","Q","R","S","T","U","V","W","X","Y","Z"]
    narr = [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26]
    i = 0
    while i < narr.length
        if num == narr[i]
            return larr[i]
        end
        i += 1
    end
end

def strconv2(strarr)
    narr = []
    i = 0
    while i < strarr.length
        narr << numconv(strarr[i])
        i += 1
    end
    return narr
end

ostr = "this is a complex string"
osstr = ostr.upcase.gsub(" ","").split(//)
key = "hello world"
narr = gen_key_string(key,ostr)
nosstr =  strconv(osstr)
nnarr = strconv(narr)
narr3 = stradd(nosstr,nnarr)
narr4 = strshort(narr3)
narr5 = strconv2(narr4)
puts narr5