Cómo hacer un Hello World! en distintos lenguajes de programación.

El Hello World es un ejercicio básico de programación. Casi en cualquier lenguaje de programación que estudies empezarás en la primera lección programando uno. Aquí te dejo diversos ejemplos en distintos lenguajes
, lo que además te permitirá ver algunas de las pequeñas diferencias que hay entre ellos.

ASP:

Response.Write "Hello World!" 

Script de Bash:

#!/bin/bash
echo "Hello, World!" 

C:

#include 
main(){
  printf ("Hello World!\n");
}

C++:

#include 
using namespace std;
void main(){
  cout << "Hello World!" << endl;
}

C#:

using System;
namespace HelloWorld
{
    class Hello 
    {
        static void Main() 
        {
            Console.WriteLine("Hello World!");            
        }
    }
}

Java:

class hellWorldJava{
  public static void main(String args[]){
    System.out.println("Hello World!");
  }
}

Javascript:

window.alert( 'Hello, world!' );

Objective C:

#import 

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        // insert code here...
        NSLog(@"Hello, World!");
    }
    return 0;
}

Perl:

#!/usr/bin/perl
print “Hello World.\n”;

PHP:

echo "Hello World!";

Script de Powershell:

$strString = "Hello World"
write-host $strString

Python:

print "Hello, World!"

R:

print("Hello World!", quote = FALSE)

Ruby:

puts 'Hello world'

Usando SHA-1 en C y C++

Estaba trasteando en C estos días como ejercicio y se me ha ocurrido utilizar una función de resumen (hash) SHA-1. Como el tema es profundamente complejo, lo que he hecho ha sido buscar una ya creada, dado que al tratarde de un algoritmo creado en 1995 existen múltiples. Voy a compartir el que he encontrado por ahí que funciona bien:

/* sha1.c : Implementation of the Secure Hash Algorithm */

/* SHA: NIST's Secure Hash Algorithm */

/*	This version written November 2000 by David Ireland of 
	DI Management Services Pty Limited <code@di-mgt.com.au>

	Adapted from code in the Python Cryptography Toolkit, 
	version 1.0.0 by A.M. Kuchling 1995.
*/

/* AM Kuchling's posting:- 
   Based on SHA code originally posted to sci.crypt by Peter Gutmann
   in message <30ajo5$oe8@ccu2.auckland.ac.nz>.
   Modified to test for endianness on creation of SHA objects by AMK.
   Also, the original specification of SHA was found to have a weakness
   by NSA/NIST.  This code implements the fixed version of SHA.
*/

/* Here's the first paragraph of Peter Gutmann's posting:
   
The following is my SHA (FIPS 180) code updated to allow use of the "fixed"
SHA, thanks to Jim Gillogly and an anonymous contributor for the information on
what's changed in the new version.  The fix is a simple change which involves
adding a single rotate in the initial expansion function.  It is unknown
whether this is an optimal solution to the problem which was discovered in the
SHA or whether it's simply a bandaid which fixes the problem with a minimum of
effort (for example the reengineering of a great many Capstone chips).
*/

/* h files included here to make this just one file ... */

/* global.h */

#ifndef _GLOBAL_H_
#define _GLOBAL_H_ 1

/* POINTER defines a generic pointer type */
typedef unsigned char *POINTER;

/* UINT4 defines a four byte word */
typedef unsigned long int UINT4;

/* BYTE defines a unsigned character */
typedef unsigned char BYTE;

#ifndef TRUE
  #define FALSE	0
  #define TRUE	( !FALSE )
#endif /* TRUE */

#endif /* end _GLOBAL_H_ */

/* sha.h */

#ifndef _SHA_H_
#define _SHA_H_ 1

/* #include "global.h" */

/* The structure for storing SHS info */

typedef struct 
{
	UINT4 digest[ 5 ];            /* Message digest */
	UINT4 countLo, countHi;       /* 64-bit bit count */
	UINT4 data[ 16 ];             /* SHS data buffer */
	int Endianness;
} SHA_CTX;

/* Message digest functions */

void SHAInit(SHA_CTX *);
void SHAUpdate(SHA_CTX *, BYTE *buffer, int count);
void SHAFinal(BYTE *output, SHA_CTX *);

#endif /* end _SHA_H_ */

/* endian.h */

#ifndef _ENDIAN_H_
#define _ENDIAN_H_ 1

void endianTest(int *endianness);

#endif /* end _ENDIAN_H_ */

/* sha.c */

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

static void SHAtoByte(BYTE *output, UINT4 *input, unsigned int len);

/* The SHS block size and message digest sizes, in bytes */

#define SHS_DATASIZE    64
#define SHS_DIGESTSIZE  20


/* The SHS f()-functions.  The f1 and f3 functions can be optimized to
   save one boolean operation each - thanks to Rich Schroeppel,
   rcs@cs.arizona.edu for discovering this */

/*#define f1(x,y,z) ( ( x & y ) | ( ~x & z ) )          // Rounds  0-19 */
#define f1(x,y,z)   ( z ^ ( x & ( y ^ z ) ) )           /* Rounds  0-19 */
#define f2(x,y,z)   ( x ^ y ^ z )                       /* Rounds 20-39 */
/*#define f3(x,y,z) ( ( x & y ) | ( x & z ) | ( y & z ) )   // Rounds 40-59 */
#define f3(x,y,z)   ( ( x & y ) | ( z & ( x | y ) ) )   /* Rounds 40-59 */
#define f4(x,y,z)   ( x ^ y ^ z )                       /* Rounds 60-79 */

/* The SHS Mysterious Constants */

#define K1  0x5A827999L                                 /* Rounds  0-19 */
#define K2  0x6ED9EBA1L                                 /* Rounds 20-39 */
#define K3  0x8F1BBCDCL                                 /* Rounds 40-59 */
#define K4  0xCA62C1D6L                                 /* Rounds 60-79 */

/* SHS initial values */

#define h0init  0x67452301L
#define h1init  0xEFCDAB89L
#define h2init  0x98BADCFEL
#define h3init  0x10325476L
#define h4init  0xC3D2E1F0L

/* Note that it may be necessary to add parentheses to these macros if they
   are to be called with expressions as arguments */
/* 32-bit rotate left - kludged with shifts */

#define ROTL(n,X)  ( ( ( X ) << n ) | ( ( X ) >> ( 32 - n ) ) )

/* The initial expanding function.  The hash function is defined over an
   80-UINT2 expanded input array W, where the first 16 are copies of the input
   data, and the remaining 64 are defined by

        W[ i ] = W[ i - 16 ] ^ W[ i - 14 ] ^ W[ i - 8 ] ^ W[ i - 3 ]

   This implementation generates these values on the fly in a circular
   buffer - thanks to Colin Plumb, colin@nyx10.cs.du.edu for this
   optimization.

   The updated SHS changes the expanding function by adding a rotate of 1
   bit.  Thanks to Jim Gillogly, jim@rand.org, and an anonymous contributor
   for this information */

#define expand(W,i) ( W[ i & 15 ] = ROTL( 1, ( W[ i & 15 ] ^ W[ (i - 14) & 15 ] ^ \
                                                 W[ (i - 8) & 15 ] ^ W[ (i - 3) & 15 ] ) ) )


/* The prototype SHS sub-round.  The fundamental sub-round is:

        a' = e + ROTL( 5, a ) + f( b, c, d ) + k + data;
        b' = a;
        c' = ROTL( 30, b );
        d' = c;
        e' = d;

   but this is implemented by unrolling the loop 5 times and renaming the
   variables ( e, a, b, c, d ) = ( a', b', c', d', e' ) each iteration.
   This code is then replicated 20 times for each of the 4 functions, using
   the next 20 values from the W[] array each time */

#define subRound(a, b, c, d, e, f, k, data) \
    ( e += ROTL( 5, a ) + f( b, c, d ) + k + data, b = ROTL( 30, b ) )

/* Initialize the SHS values */

void SHAInit(SHA_CTX *shsInfo)
{
    endianTest(&shsInfo->Endianness);
    /* Set the h-vars to their initial values */
    shsInfo->digest[ 0 ] = h0init;
    shsInfo->digest[ 1 ] = h1init;
    shsInfo->digest[ 2 ] = h2init;
    shsInfo->digest[ 3 ] = h3init;
    shsInfo->digest[ 4 ] = h4init;

    /* Initialise bit count */
    shsInfo->countLo = shsInfo->countHi = 0;
}


/* Perform the SHS transformation.  Note that this code, like MD5, seems to
   break some optimizing compilers due to the complexity of the expressions
   and the size of the basic block.  It may be necessary to split it into
   sections, e.g. based on the four subrounds

   Note that this corrupts the shsInfo->data area */

static void SHSTransform( digest, data )
     UINT4 *digest, *data ;
    {
    UINT4 A, B, C, D, E;     /* Local vars */
    UINT4 eData[ 16 ];       /* Expanded data */

    /* Set up first buffer and local data buffer */
    A = digest[ 0 ];
    B = digest[ 1 ];
    C = digest[ 2 ];
    D = digest[ 3 ];
    E = digest[ 4 ];
    memcpy( (POINTER)eData, (POINTER)data, SHS_DATASIZE );

    /* Heavy mangling, in 4 sub-rounds of 20 interations each. */
    subRound( A, B, C, D, E, f1, K1, eData[  0 ] );
    subRound( E, A, B, C, D, f1, K1, eData[  1 ] );
    subRound( D, E, A, B, C, f1, K1, eData[  2 ] );
    subRound( C, D, E, A, B, f1, K1, eData[  3 ] );
    subRound( B, C, D, E, A, f1, K1, eData[  4 ] );
    subRound( A, B, C, D, E, f1, K1, eData[  5 ] );
    subRound( E, A, B, C, D, f1, K1, eData[  6 ] );
    subRound( D, E, A, B, C, f1, K1, eData[  7 ] );
    subRound( C, D, E, A, B, f1, K1, eData[  8 ] );
    subRound( B, C, D, E, A, f1, K1, eData[  9 ] );
    subRound( A, B, C, D, E, f1, K1, eData[ 10 ] );
    subRound( E, A, B, C, D, f1, K1, eData[ 11 ] );
    subRound( D, E, A, B, C, f1, K1, eData[ 12 ] );
    subRound( C, D, E, A, B, f1, K1, eData[ 13 ] );
    subRound( B, C, D, E, A, f1, K1, eData[ 14 ] );
    subRound( A, B, C, D, E, f1, K1, eData[ 15 ] );
    subRound( E, A, B, C, D, f1, K1, expand( eData, 16 ) );
    subRound( D, E, A, B, C, f1, K1, expand( eData, 17 ) );
    subRound( C, D, E, A, B, f1, K1, expand( eData, 18 ) );
    subRound( B, C, D, E, A, f1, K1, expand( eData, 19 ) );

    subRound( A, B, C, D, E, f2, K2, expand( eData, 20 ) );
    subRound( E, A, B, C, D, f2, K2, expand( eData, 21 ) );
    subRound( D, E, A, B, C, f2, K2, expand( eData, 22 ) );
    subRound( C, D, E, A, B, f2, K2, expand( eData, 23 ) );
    subRound( B, C, D, E, A, f2, K2, expand( eData, 24 ) );
    subRound( A, B, C, D, E, f2, K2, expand( eData, 25 ) );
    subRound( E, A, B, C, D, f2, K2, expand( eData, 26 ) );
    subRound( D, E, A, B, C, f2, K2, expand( eData, 27 ) );
    subRound( C, D, E, A, B, f2, K2, expand( eData, 28 ) );
    subRound( B, C, D, E, A, f2, K2, expand( eData, 29 ) );
    subRound( A, B, C, D, E, f2, K2, expand( eData, 30 ) );
    subRound( E, A, B, C, D, f2, K2, expand( eData, 31 ) );
    subRound( D, E, A, B, C, f2, K2, expand( eData, 32 ) );
    subRound( C, D, E, A, B, f2, K2, expand( eData, 33 ) );
    subRound( B, C, D, E, A, f2, K2, expand( eData, 34 ) );
    subRound( A, B, C, D, E, f2, K2, expand( eData, 35 ) );
    subRound( E, A, B, C, D, f2, K2, expand( eData, 36 ) );
    subRound( D, E, A, B, C, f2, K2, expand( eData, 37 ) );
    subRound( C, D, E, A, B, f2, K2, expand( eData, 38 ) );
    subRound( B, C, D, E, A, f2, K2, expand( eData, 39 ) );

    subRound( A, B, C, D, E, f3, K3, expand( eData, 40 ) );
    subRound( E, A, B, C, D, f3, K3, expand( eData, 41 ) );
    subRound( D, E, A, B, C, f3, K3, expand( eData, 42 ) );
    subRound( C, D, E, A, B, f3, K3, expand( eData, 43 ) );
    subRound( B, C, D, E, A, f3, K3, expand( eData, 44 ) );
    subRound( A, B, C, D, E, f3, K3, expand( eData, 45 ) );
    subRound( E, A, B, C, D, f3, K3, expand( eData, 46 ) );
    subRound( D, E, A, B, C, f3, K3, expand( eData, 47 ) );
    subRound( C, D, E, A, B, f3, K3, expand( eData, 48 ) );
    subRound( B, C, D, E, A, f3, K3, expand( eData, 49 ) );
    subRound( A, B, C, D, E, f3, K3, expand( eData, 50 ) );
    subRound( E, A, B, C, D, f3, K3, expand( eData, 51 ) );
    subRound( D, E, A, B, C, f3, K3, expand( eData, 52 ) );
    subRound( C, D, E, A, B, f3, K3, expand( eData, 53 ) );
    subRound( B, C, D, E, A, f3, K3, expand( eData, 54 ) );
    subRound( A, B, C, D, E, f3, K3, expand( eData, 55 ) );
    subRound( E, A, B, C, D, f3, K3, expand( eData, 56 ) );
    subRound( D, E, A, B, C, f3, K3, expand( eData, 57 ) );
    subRound( C, D, E, A, B, f3, K3, expand( eData, 58 ) );
    subRound( B, C, D, E, A, f3, K3, expand( eData, 59 ) );

    subRound( A, B, C, D, E, f4, K4, expand( eData, 60 ) );
    subRound( E, A, B, C, D, f4, K4, expand( eData, 61 ) );
    subRound( D, E, A, B, C, f4, K4, expand( eData, 62 ) );
    subRound( C, D, E, A, B, f4, K4, expand( eData, 63 ) );
    subRound( B, C, D, E, A, f4, K4, expand( eData, 64 ) );
    subRound( A, B, C, D, E, f4, K4, expand( eData, 65 ) );
    subRound( E, A, B, C, D, f4, K4, expand( eData, 66 ) );
    subRound( D, E, A, B, C, f4, K4, expand( eData, 67 ) );
    subRound( C, D, E, A, B, f4, K4, expand( eData, 68 ) );
    subRound( B, C, D, E, A, f4, K4, expand( eData, 69 ) );
    subRound( A, B, C, D, E, f4, K4, expand( eData, 70 ) );
    subRound( E, A, B, C, D, f4, K4, expand( eData, 71 ) );
    subRound( D, E, A, B, C, f4, K4, expand( eData, 72 ) );
    subRound( C, D, E, A, B, f4, K4, expand( eData, 73 ) );
    subRound( B, C, D, E, A, f4, K4, expand( eData, 74 ) );
    subRound( A, B, C, D, E, f4, K4, expand( eData, 75 ) );
    subRound( E, A, B, C, D, f4, K4, expand( eData, 76 ) );
    subRound( D, E, A, B, C, f4, K4, expand( eData, 77 ) );
    subRound( C, D, E, A, B, f4, K4, expand( eData, 78 ) );
    subRound( B, C, D, E, A, f4, K4, expand( eData, 79 ) );

    /* Build message digest */
    digest[ 0 ] += A;
    digest[ 1 ] += B;
    digest[ 2 ] += C;
    digest[ 3 ] += D;
    digest[ 4 ] += E;
    }

/* When run on a little-endian CPU we need to perform byte reversal on an
   array of long words. */

static void longReverse(UINT4 *buffer, int byteCount, int Endianness )
{
    UINT4 value;

    if (Endianness==TRUE) return;
    byteCount /= sizeof( UINT4 );
    while( byteCount-- )
        {
        value = *buffer;
        value = ( ( value & 0xFF00FF00L ) >> 8  ) | \
                ( ( value & 0x00FF00FFL ) << 8 );
        *buffer++ = ( value << 16 ) | ( value >> 16 );
        }
}

/* Update SHS for a block of data */

void SHAUpdate(SHA_CTX *shsInfo, BYTE *buffer, int count)
{
    UINT4 tmp;
    int dataCount;

    /* Update bitcount */
    tmp = shsInfo->countLo;
    if ( ( shsInfo->countLo = tmp + ( ( UINT4 ) count << 3 ) ) < tmp )
        shsInfo->countHi++;             /* Carry from low to high */
    shsInfo->countHi += count >> 29;

    /* Get count of bytes already in data */
    dataCount = ( int ) ( tmp >> 3 ) & 0x3F;

    /* Handle any leading odd-sized chunks */
    if( dataCount )
        {
        BYTE *p = ( BYTE * ) shsInfo->data + dataCount;

        dataCount = SHS_DATASIZE - dataCount;
        if( count < dataCount )
            {
            memcpy( p, buffer, count );
            return;
            }
        memcpy( p, buffer, dataCount );
        longReverse( shsInfo->data, SHS_DATASIZE, shsInfo->Endianness);
        SHSTransform( shsInfo->digest, shsInfo->data );
        buffer += dataCount;
        count -= dataCount;
        }

    /* Process data in SHS_DATASIZE chunks */
    while( count >= SHS_DATASIZE )
        {
        memcpy( (POINTER)shsInfo->data, (POINTER)buffer, SHS_DATASIZE );
        longReverse( shsInfo->data, SHS_DATASIZE, shsInfo->Endianness );
        SHSTransform( shsInfo->digest, shsInfo->data );
        buffer += SHS_DATASIZE;
        count -= SHS_DATASIZE;
        }

    /* Handle any remaining bytes of data. */
    memcpy( (POINTER)shsInfo->data, (POINTER)buffer, count );
    }

/* Final wrapup - pad to SHS_DATASIZE-byte boundary with the bit pattern
   1 0* (64-bit count of bits processed, MSB-first) */

void SHAFinal(BYTE *output, SHA_CTX *shsInfo)
{
    int count;
    BYTE *dataPtr;

    /* Compute number of bytes mod 64 */
    count = ( int ) shsInfo->countLo;
    count = ( count >> 3 ) & 0x3F;

    /* Set the first char of padding to 0x80.  This is safe since there is
       always at least one byte free */
    dataPtr = ( BYTE * ) shsInfo->data + count;
    *dataPtr++ = 0x80;

    /* Bytes of padding needed to make 64 bytes */
    count = SHS_DATASIZE - 1 - count;

    /* Pad out to 56 mod 64 */
    if( count < 8 )
        {
        /* Two lots of padding:  Pad the first block to 64 bytes */
        memset( dataPtr, 0, count );
        longReverse( shsInfo->data, SHS_DATASIZE, shsInfo->Endianness );
        SHSTransform( shsInfo->digest, shsInfo->data );

        /* Now fill the next block with 56 bytes */
        memset( (POINTER)shsInfo->data, 0, SHS_DATASIZE - 8 );
        }
    else
        /* Pad block to 56 bytes */
        memset( dataPtr, 0, count - 8 );

    /* Append length in bits and transform */
    shsInfo->data[ 14 ] = shsInfo->countHi;
    shsInfo->data[ 15 ] = shsInfo->countLo;

    longReverse( shsInfo->data, SHS_DATASIZE - 8, shsInfo->Endianness );
    SHSTransform( shsInfo->digest, shsInfo->data );

	/* Output to an array of bytes */
	SHAtoByte(output, shsInfo->digest, SHS_DIGESTSIZE);

	/* Zeroise sensitive stuff */
	memset((POINTER)shsInfo, 0, sizeof(shsInfo));
}

static void SHAtoByte(BYTE *output, UINT4 *input, unsigned int len)
{	/* Output SHA digest in byte array */
	unsigned int i, j;

	for(i = 0, j = 0; j < len; i++, j += 4) 
	{
        output[j+3] = (BYTE)( input[i]        & 0xff);
        output[j+2] = (BYTE)((input[i] >> 8 ) & 0xff);
        output[j+1] = (BYTE)((input[i] >> 16) & 0xff);
        output[j  ] = (BYTE)((input[i] >> 24) & 0xff);
	}
}


unsigned char digest[20];
unsigned char message[3] = {'a', 'b', 'c' };
unsigned char *mess56 = 
	"abcdbcdecdefdefgefghfghighijhijkijkljklmklmnlmnomnopnopq";

/* Correct solutions from FIPS PUB 180-1 */
char *dig1 = "A9993E36 4706816A BA3E2571 7850C26C 9CD0D89D";
char *dig2 = "84983E44 1C3BD26E BAAE4AA1 F95129E5 E54670F1";
char *dig3 = "34AA973C D4C4DAA4 F61EEB2B DBAD2731 6534016F";

/* Output should look like:-
 a9993e36 4706816a ba3e2571 7850c26c 9cd0d89d
 A9993E36 4706816A BA3E2571 7850C26C 9CD0D89D <= correct
 84983e44 1c3bd26e baae4aa1 f95129e5 e54670f1
 84983E44 1C3BD26E BAAE4AA1 F95129E5 E54670F1 <= correct
 34aa973c d4c4daa4 f61eeb2b dbad2731 6534016f
 34AA973C D4C4DAA4 F61EEB2B DBAD2731 6534016F <= correct
*/

main()
{
	SHA_CTX sha;
	int i;
	BYTE big[1000];

	SHAInit(&sha);
	SHAUpdate(&sha, message, 3);
	SHAFinal(digest, &sha);

	for (i = 0; i < 20; i++)
	{
		if ((i % 4) == 0) printf(" ");
		printf("%02x", digest[i]);
	}
	printf("\n");
	printf(" %s <= correct\n", dig1);

	SHAInit(&sha);
	SHAUpdate(&sha, mess56, 56);
	SHAFinal(digest, &sha);

	for (i = 0; i < 20; i++)
	{
		if ((i % 4) == 0) printf(" ");
		printf("%02x", digest[i]);
	}
	printf("\n");
	printf(" %s <= correct\n", dig2);

	/* Fill up big array */
	for (i = 0; i < 1000; i++)
		big[i] = 'a';

	SHAInit(&sha);
	/* Digest 1 million x 'a' */
	for (i = 0; i < 1000; i++)
		SHAUpdate(&sha, big, 1000);
	SHAFinal(digest, &sha);

	for (i = 0; i < 20; i++)
	{
		if ((i % 4) == 0) printf(" ");
		printf("%02x", digest[i]);
	}
	printf("\n");
	printf(" %s <= correct\n", dig3);

	return 0;
}

/* endian.c */

void endianTest(int *endian_ness)
{
	if((*(unsigned short *) ("#S") >> 8) == '#')
	{
		/* printf("Big endian = no change\n"); */
		*endian_ness = !(0);
	}
	else
	{
		/* printf("Little endian = swap\n"); */
		*endian_ness = 0;
	}
}

He dejado todos los comentarios, aunque se os pueda hacer coñazo, por respeto a los creadores originales. La función original la podéis consultar aquí.

Para C++ por otra parte, podéis disfrutar de la librería libre Crypto++ con múltiples algoritmos, que podéis encontrar en este enlace.

Programa en C que imprime el código ASCII// Imprimir letra ñ en C y CPP

Así, a lo tonto, voy a hacerme aquí un típico ejemplo académico de C. No se si aportará mucho o si le interesará a alguien, pero lo hago por una cuestión más bien curricular (vamos, que he mandado curriculums a academias para dar clases de c y quiero que vean que podría dar clase… sí, lo digo así de sincero).

Lo primero es comentar que cuando uno hace un programa en C en castellano se va a topar con una “coñetta” muy jodona… Los caracteres ñ y Ñ no se imprimen si los pones a saco directamente en una cadena. Es decir, la instrucción “printf(“coñetta”);” saldría con algún símbolo raro en lugar de la Ñ. Pero don’t worry, imprimir una ñ, minúscula o mayúscula en C y C++ no requiere ser ingeniero informático. Y hasta tenéis varias opciones que podréis ver en el siguiente ejemplo:

void main(){
  printf(" %c ",164);//imprime una ñ minúscula
  printf(" %c ",165);//imprime una Ñ mayúscula
  printf(" xA4 ");//imprime una ñ minúscula
  printf(" xA5 ");//imprime una Ñ mayúscula
  printf(" co%co ",164);//imprime coño
  printf(" cumpleaxA4os ");//imprime cumpleaños
}

En los dos primeros ejemplos estaríamos diciendo “imprime una variable de caracter con el caracter cuyo valor ASCII sea 164” (165 en el segundo caso). Si estás mirando esto supongo que ya sabes algo de C, ya sabes que la función printf imprime datos en pantalla y que %c es una variable de caracter, y 164 y 165 no serían más que los parámetros con el valor ASCII.

En los casos 3 y 4 realmente es lo mismo. La instrucción viene a decir “imprime el caracter cuyo valor ASCII hexadecimal es A4” (A5 en el caso de la mayúscula). En cualquier caso ambos ejemplos hacen referencia a la tabla de valores ASCII.

Claro, el valor ASCII en principio es ese si nos ceñimos a Windows/MS-DOS. Pero en un SO Apple, BSD o Linux podría variar dependiendo de la distribución. Con este sencillo programa podéis imprimir toda la tabla ASCII para comprobarlo:

#include stdio.h;
void main(){
  int i; //variable contador para el bucle
  printf(“C%cdigo\t-\tLetrann”, 162);

  for(i=0; i<256; i++)//bucle for que recorre los 256 caracteres ASCII
    {
      printf(“%d\t-\t%c\n”, i, i);//imprimimos el número y el caracter
    }
}

Y así a lo tonto ya tenés in práctico programa que os imprimirá toda la tabla ASCII. Y si soy capaz de escribir esto a las cinco de la mañana volviendo de un pub, imaginad cómo puedo dar clase descansado y preparado.