Write a program in c++ that reverses the C-style string pointed to by s. * * @pa

Question

Write a program in c++ that reverses the C-style string pointed to by s.
*
* @param s a pointer to the character in a C-style string.
*
* NOTE: for this assignment, you can only use ++, --,
* = (assignment), ==,!= (comparison) and pointer subtraction
* (p1 - p2). You cannot use pointer arithmetic (s + i), or
* array notation (s[i]). In fact, you cannot have ANY integer
* variables or literals in your code. You also cannot use ANY
* standard library functions including strlen.

cpp file:

#include <string>
using namespace std;

#include "h27.h"

void reverse(char * s)

{

// Add your code here

}

This is the implementation file:

#ifndef H27_H_
#define H27_H_

void reverse(char * s);

#endif
// DO NOT CHANGE ANY OF THESE LINES
#define strlen(s) static_assert(false, "strlen not allowed");
#define strcat(d, s) static_assert(false, "strcat not allowed");
#define strcpy(d, s) static_assert(false, "strcpy not allowed");
#define string static_assert(false, "string not allowed");

Can someone do this and explain your steps please? Thanks.

Explanation / Answer

Solution:

reverse.cpp:

#include <string>
#include <iostream>
using namespace std;

#include "h27.h"

void reverse(char *s)

{
   //initially two temporary pointers are teken
   char *pointer1 = s;
   char *pointer2 = s;
  
   //moving the first pointer till null charcter found(cstring ends with null charcter)
   while(*pointer1!=''){
       pointer1++;
   }
  
   //decreasing one postion back.so pointer1 is present at last charcter of the cstring
   pointer1--;
  
   /**
   *
   * here swaping the first charcter and last charcter
   * then we are moving pointer1 backward pointer2 forward
   * till both are colide.when collision occurs pointer1>pointer2 condition fails
   * Then loop will break.And string is reversed
   *
   * */
   while(pointer1>pointer2){
      
       char temp = *pointer2;
       *pointer2 = *pointer1;
       *pointer1 = temp;
       pointer2++;
       pointer1--;
      
   }
  
   //here we are printing the string
   cout << "Reverse of given string is:" << s << endl;
  

}

int main(){
  
   //here 2 charcter arrays are taken to test the reverse function
   char cstring[] = {'H','e','l','l','o',''};
   char cstring1[] = {'H','e','l','l',''};
  
   //calling the reverse function
   reverse(cstring);
   reverse(cstring1);
  
   return 0;
}

h27.h:

#ifndef H27_H_
#define H27_H_

void reverse(char * s);

#endif
// DO NOT CHANGE ANY OF THESE LINES
#define strlen(s) static_assert(false, "strlen not allowed");
#define strcat(d, s) static_assert(false, "strcat not allowed");
#define strcpy(d, s) static_assert(false, "strcpy not allowed");
#define string static_assert(false, "string not allowed");

sample output:

Reverse of given string is:olleH
Reverse of given string is:lleH

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