#include <stdio.h>
#include <string.h>
 
void revertir(char * cadena)
{
	unsigned int i = 0;
	char temp = NULL;
	unsigned int len = strlen(cadena);
 
	for (; i < len / 2; i++)
	{
		temp = cadena[i];
		cadena[i] = cadena[len - i - 1];
		cadena[len - i - 1] = temp;
	}
}
 
int main(int argc, char * argv[])
{
	char cadena[] = "Esto es una cadena";
 
	printf("%s\n", cadena);
	revertir(cadena);
	printf("%s\n", cadena);
 
	getchar();
	return 0;
}
 

 
#define BYTE unsigned char
 
BYTE* reverse(BYTE* pbyData, size_t szSize) {
    size_t i = 0x0;
    if (szSize > 1)
        for (;i < --szSize; i++) {
            pbyData[i]      ^= pbyData[szSize];
            pbyData[szSize] ^= pbyData[i];
            pbyData[i]      ^= pbyData[szSize];
        }
    return pbyData;
}
 
int main()
{
    char  szCadena[]  = "Hola Mundo";
    printf("%s\n", reverse((BYTE*)szCadena, strlen(szCadena)));
    getchar();
    return 0;
}
 
 

char * Revertir(char *Cadena, int tam)
{
 
	int i;
	char *tmp;
 
	tmp = (char*)malloc(tam);
 
	for (i = tam - 1; i >= 0; i--)
	{
		tmp[(tam-1)-i] = Cadena[i];
	}
 
	tmp[tam] = '\0';
 
	return tmp;
}

char *invertir(char const *cad, int num_chars)
{
   char *tmp;
   int i;
 
   tmp = malloc(num_chars + 1);
 
   for (i = 0; i < num_chars; i++)
      tmp[i] = cad[num_chars - 1 - i];
   tmp[i] = '\0';
 
   return tmp;
}

char *strrev(char *s);