Write a program that reads a string \(\texttt{STR}\) from the keyboard and then adds the reverse of \(\texttt{STR}\) to its end (i.e. \(\texttt{STR}\) should contain the original string and its reverse).
You may assume that the size of the string \(\texttt{STR}\) is big enough to hold the string and its reverse.
The usage of any function of the \(\texttt{string.h}\) library is not allowed.

Running example:

#include <stdio.h>

void main()
{
	char STR[100];
	int i , j;
	
	printf("Enter a string: ");
	gets(STR);

	i = 0;
	// loop until the \0
	while (STR[i]) // go to the end of STR 
		i++;
	// j goes backward from i-1 till 0
	j = i - 1;

	while (j >= 0) // copy STR to the end of STR 
	{
		STR[i] = STR[j];
		i++;
		j--;
	}
	// end of string
	STR[i] = '\0';

	puts(STR);
}