C program to write 5 lines to a file then print the lines except the second line
You have the right idea in write_to_file(), but print_file() is awkward.

There is no need to work a character at a time in print_file(). You can read a line at a time using fgets(buffer, sizeof(buffer), in_file).

Avoid flag variables. Here, you could use a for loop to track the line number instead.

char buffer[MAX_SIZE];
for (int i = 0; fgets(buffer, sizeof(buffer), in_file) != EOF; ++i) {
    if (i != 1) puts(buffer);
}