convert .join statement of python into c programming code example

Example 1: how to join a list of characters in python

>>> a = ['a', 'b', 'c', 'd']
>>> ''.join(a)
'abcd'

Example 2: python to c converter

import sys

def mergesort_2ndstep(l, r):
	len_l = len(l)
	len_r = len(r)
	# initializing a list of length zero
	sorted_array = []
	i,j = 0,0
	while i < len_l:
		num1 = l[i]
		for x in range(j,len_r):
			num2 = r[x]
			if num2 < num1 :
				sorted_array.append(num2)
				j += 1
		
		sorted_array.append(num1)
		i += 1

	if len(sorted_array) != len_l + len_r:
		# Checking extreme conditions
		sorted_array[i+j:] = r[j:]
	return sorted_array


def mergesort_1ststep(L,start,stop):
	# a list can be divided into two 
	# if length of list is atleast two
	if stop - start > 1:
		l = mergesort_1ststep(L,start,start + (stop-start)//2)
		r = mergesort_1ststep(L,start + (stop-start)//2,stop)
		# mergeing two lists(sorting the l and r parts)
		L[start:stop] = mergesort_2ndstep(l,r)
	return L[start:stop]

# START
List_of_nums = []
file_to_open = "input1.txt"

try:
	read_file = open(file_to_open,"r")
	write_file = open("output.txt","w")
	if read_file != None:
		# appending every num from file to list_of_nums
		for line in read_file:
			line = int(line)
			List_of_nums.append(line)
		# applying mergesort
		mergesort_1ststep(List_of_nums,0, len(List_of_nums))
		# writing to an output file
		# excluding the last element 
		k = List_of_nums.pop()
		for num in List_of_nums:
			write_file.write(f"{num}\n")
		# writing last element without next line
		write_file.write(f"{k}")
		# closing files 
		read_file.close()
		write_file.close()
except:
	print("file not found")