#if and #endif

[Arthuro]

I want to implement #if (DEBUG==1) I want an entering and exiting message to print before and after invoking decrypt()

I have no clue to how to do it...my books I so confusing and hopeless!!!

I need help!!

here is my program: A bit long it is basically encrypting and then decrypting a text using a scramble and unscramble key

#include <stdio.h>
#include <string.h>
#define LINESIZE 60
#define MIN(a,b) (((a)<(b))?(a):(b))

static const char KEY[]="qazxswedcvfrtgbnhyujmkiolp";

void decrypt(const char in[],char out[]);
void encrypt(const char in[],char out[]);
void printtext(const char t[]);
char scramble(const char c);
char unscramble(const char c);

int main(void)
{
    const char plaintext[]="Fourscore and seven years ago our fathers \
brought forth upon this continent a new nation, conceived in liberty, \
and dedicated to the proposition that all men are created equal.";

    char decrypttext[sizeof(plaintext)/sizeof(char)];
	char encrypttext[sizeof(plaintext)/sizeof(char)];
	
	printtext(plaintext);
    encrypt(plaintext,encrypttext);
	printtext(encrypttext);
	decrypt(encrypttext,decrypttext);
	printtext(decrypttext);

	if (strcmp(plaintext,decrypttext)==0)
		puts("plain same decrypttext");
    	else puts("not identical");

	return 0;
}

/*encrypt*/
void encrypt(const char in[],char out[])
{
	int k;
	
	for (k=0;in[k];k++)
		out[k]=scramble(in[k]);
	out[k]='0';
	
	return;
}

/*decrypt*/
void decrypt(const char in[],char out[])
{
	int k;
	
	for (k=0;in[k];k++)
		out[k]=unscramble(in[k]);
	out[k]='0';
	
	return;
}

/*scramble*/
char scramble(const char c)
{
	if ((c<'a')|| (c>'z')) return c;
	return KEY[c-'a'];
}

/*unscramble*/
char unscramble(const char c)
{
	int k;
	char alphabet[]="abcdefghijklmnopqrstuvwxyz";
    
	if ((c<'a')||(c>'z')) return c;

	for (k=0;k<strlen(KEY);k++)
		if (c==KEY[k]) break;
	
	return alphabet[k];
}

/*printtext*/
void printtext(const char t[])
{
	int start;
	int finish;
	int k, tmp;

	start =0;

	while (start<strlen(t))
	{
		tmp=MIN((start+LINESIZE),strlen(t));
		for (finish=tmp;finish>start;finish--)
			if ( (t[finish]==' ') || (t[finish]=='\0') ) break;

		for(k=start;k<finish;k++)
			putchar(t[k]);
		printf("\n");

		start=finish+1;    
	}
	printf("\n");

	return;
}

[Prelude]

int main(void)
{
  const char plaintext[]="Fourscore and seven years ago our fathers \
    brought forth upon this continent a new nation, conceived in liberty, \
    and dedicated to the proposition that all men are created equal.";

  char decrypttext[sizeof(plaintext)/sizeof(char)];
  char encrypttext[sizeof(plaintext)/sizeof(char)];

  printtext(plaintext);
  encrypt(plaintext,encrypttext);
  printtext(encrypttext);

#ifdef DEBUG
  fputs ( "Entering decrypt\n", stdout );
#endif
  decrypt(encrypttext,decrypttext);
#ifdef DEBUG
  fputs ( "Exiting decrypt\n", stdout );
#endif

  printtext(decrypttext);

  if (strcmp(plaintext,decrypttext)==0)
    puts("plain same decrypttext");
  else
    puts("not identical");

  return 0;
}

Now all you have to do is define DEBUG like this:

#define DEBUG

And the print statements will execute, if you comment out the above line, neither of the print statements will execute.

-Prelude