How to Properly Escape Nested Special Characters

I need to save below example sentences as a file called demo.sh.

#!/usr/bin/env bash   
xmessage This is "first sentence"
xmessage This is 'second sentence'
xmessage This is {third sentence}

The code I use in C is below:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main()
{
    system("sudo bash -c 'printf \"#!/usr/bin/env bash\n\" > /usr/share/applications/demo.sh'");
    return 0;
}

I can write the first sentence of the above 4 sentences OK into the file. But the other sentences contain special characters like single quotes, double quotes and line ending character. And this gets very difficult to escape because sudo command needs to have two nested section which I tried to wrap by ' and " separately.

How can I escape the sentences and write out to the file? It would be great to have some function because actually the file is more than 4 sentences and have many special characters.

As a note, I know I could use I/O functions of C, I want to write the file by a single system command which use sudo, printf and one line string.