Here is source code of the C Program to merge lines alternatively from 2 files & print result. The C program is successfully compiled and run on a Linux system. The program output is also shown below.

/*
* C Program that Merges Lines Alternatively from 2 Files & Print Result
*/
#include<stdio.h>
main()
{
char file1[10], file2[10];

puts("enter the name of file 1"); /*getting the names of file to be concatenated*/
scanf("%s", file1);
puts("enter the name of file 2");
scanf("%s", file2);
FILE *fptr1, *fptr2, *fptr3;
fptr1=fopen(file1, "r"); /*opening the files in read only mode*/
fptr2=fopen(file2, "r");
fptr3=fopen("merge2.txt", "w+"); /*opening a new file in write,update mode*/
char str1[200];
char ch1, ch2;
int n = 0, w = 0;
while (((ch1=fgetc(fptr1)) != EOF) && ((ch2 = fgetc(fptr2)) != EOF))
{
if (ch1 != EOF) /*getting lines in alternately from two files*/
{
ungetc(ch1, fptr1);
fgets(str1, 199, fptr1);
fputs(str1, fptr3);
if (str1[0] != 'n')
n++; /*counting no. of lines*/
}
if (ch2 != EOF)
{
ungetc(ch2, fptr2);
fgets(str1, 199, fptr2);
fputs(str1, fptr3);
if (str1[0] != 'n')
n++; /*counting no.of lines*/
}
}
rewind(fptr3);
while ((ch1 = fgetc(fptr3)) != EOF) /*countig no.of words*/
{
ungetc(ch1, fptr3);
fscanf(fptr3, "%s", str1);
if (str1[0] != ' ' || str1[0] != 'n')
w++;
}
fprintf(fptr3, "\n\n number of lines = %d n number of words is = %d\n", n, w - 1);
/*appendig comments in the concatenated file*/
fclose(fptr1);
fclose(fptr2);
fclose(fptr3);
}


$ cc pgm51.c
$ a.out
enter the name of file 1
c.txt
enter the name of file 2
a.txt
$ vi merge2.txt
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number of lines = 4
number of words is = 114