CODEWITHSUNDEEP
c++arraysstringpointers
Ayushi bhardwaj
Ayushi bhardwaj

Reputation: 451

Reversing string using character array

I wrote a program to reverse string where the string is a character array. The program is :

#include<iostream>
void rev(char *str)
{
  char *end;
  end = str;// end will now point to the same address of str
  // now we need to incremet the end pointer upto it encounter null
  if(str)// this checks if the string is present or not
  {
    while(*end)
      ++end;
    --end;// set one character back, since last character is null
    // swap characters from start of string with the end of the string
    // until the pointers meet in middle.
    while(str < end)
    {
      char temp = *str;
      *str++ = *end;
      *end-- = temp;
    }
  }
  std::cout<<"\n The reversed string is : \n";
  std::cout<<str<<std::endl;
}
int main()
{
  char str[500];
  std::cout<<"\n Enter the string : ";
  std::cin.getline(str, sizeof(str));
  rev(str);
  return 0;
}

One output instance is :

Enter the string : asdfgh

 The reversed string is : 
dsa

I want to solve this problem inplace and using character array.

There are many solutions available on internet. I have seen them. But I want to know where I'm going wrong with this implementation. If there is some extra increment in str. I want to know how to correct it.

Upvotes: 0

Views: 495

Answers (4)

surajs1n
surajs1n

Reputation: 1583

Well, the error is that you kept on increasing the str pointer and after that decreasing the end pointer, which finally met somewhere at the middle of the string. And right after, you printed out the string which starts somewhere from the middle in reverse order. So, I would suggest to do as follows:

#include<iostream>
void rev(char *str) {
  char *end;
  end = str;

  if(str) {
    while(*end)
        ++end;
    --end;

    while(str < end) {
      char temp = *str;
      *str++ = *end;
      *end-- = temp;
    }
  }
  /* Don't print the string here itself */
}

int main() {
  char str[500];
  std::cout<<"\n Enter the string : ";
  std::cin.getline(str, sizeof(str));
  rev(str);

  /* Print your string here */
  std::cout<<"\n The reversed string is : \n";
  std::cout<<str<<std::endl;
  return 0;
}

OUTPUT:

 Enter the string : qwertyuiop

 The reversed string is : 
poiuytrewq

Upvotes: 4

Ami Tavory
Ami Tavory

Reputation: 76326

Well, since this is tagged c++, you should note that you can do this as

void rev(char* str)
{
    std::reverse(str, str + strlen(str));
}

Looking at the documentation for std::reverse you can deduce that it does it in place.

Upvotes: 3

Han Arantes
Han Arantes

Reputation: 775

Try this: 

#include<bits/stdc++.h>

int main()
{
    char str[500], revstr[500];
    int i,j,len;
    std::cout<<"\n Enter the string : ";
    std::cin.getline(str, sizeof(str));

    //reverse str
    len = strlen(str);
    for(i=len-1, j=0; i>=0; i--, j++){
        revstr[j]=len[i];
    }
    revstr[j] = '\0'; //marks end of string

    std::cout<<"\n The reversed string is : \n";
    std::cout<<revstr<<std::endl;

  return 0;
}

Upvotes: 0

erip
erip

Reputation: 16935

I think you're making the problem too confusing.

void reverse(char* s) {
  // return if s is nullptr
  if(!s) return;

  size_t len = strlen(s);

  // swap ith from front with ith from back
  for(size_t i = 0; i < len/2; ++i) {
    char temp = s[i];
    s[i] = s[len - i - 1];
    s[len - i - 1] = temp;
  }
}

Upvotes: 5

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