gistfile1.h

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define BUFFERSIZE 1024
//
void sample(void)
{
	// size_t is unsigned int type.
	size_t str_size = 0, i = 0;
	int  alphabet = 0;
	// string: char array
	// You should initialize them for safety.
	char word[BUFFERSIZE] = "", wordindex[BUFFERSIZE] = "";
	// You may need a buffer.
	char buffer[BUFFERSIZE] = "";
	printf("Enter your desired word or sentence: ");
	// string word, its name is a pointer.
	//scanf("%s", word);
	// get a string for a line.
	gets(word);
	// let strlen return size_t type.
	str_size = strlen(word);
	for (i = 0; i < str_size; i ++)
	{
		alphabet = (int)word[i];
		itoa( alphabet, buffer, 2);
		strcat( wordindex, buffer);
	}
	// print binary string.
	printf("%s\n", wordindex);
}
void main(void)
{
	sample();
	system("PAUSE");
}