How to write c++ code to reverse a string without using inbuilt function?

Question

I have write this code. It does not show any error but string is not reversed.please let me know where i have made the mistake? I'm using codeblock to write code and GCC compiler. I have created two functions reverseString and printString, the printString function is working but reverseString is not working. what can i do?

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

void reverseString(string s, int iNode, int lNode){
    while(iNode < lNode){
        char temp = s[iNode];
        s[iNode] = s[lNode];
        s[lNode] = temp;
        iNode++;
        lNode--;
    }
}

void printString(string s, int n){

    for(int i=0; i<n; i++){
        cout << s[i];
        cout << endl;
    }
}

int main() {
  string s;
  cout << "Type String To Reverse: \n";
  cin >> s;
  cout << "String In Actual Order: \n";
  printString(s,s.length());
  reverseString(s, 0, s.length()-1);
  cout << "String In Reverse Order: \n";
  printString(s,s.length());

  return 0;
}

You passed string by value, meaning you created a full copy of a string and made some operations on it, meanwhile your initial string remained unchanged. Your reverseString func should have this signature: `void reverseString(string& s, int iNode, int lNode)` . [Also see here](https://stackoverflow.com/questions/373419/whats-the-difference-between-passing-by-reference-vs-passing-by-value?noredirect=1&lq=1) — Learpcs, May 06 '22 at 19:12

Vlad from Moscow · Answer 1 · 2022-05-06T19:42:56.680

This function accepts an object of the type std::string by value

void reverseString(string s, int iNode, int lNode){
    while(iNode < lNode){
        char temp = s[iNode];
        s[iNode] = s[lNode];
        s[lNode] = temp;
        iNode++;
        lNode--;
    }
}

It means that it deals with a copy of the string used as an argument and changes the copy instead of the original string.

You have to declare the parameter as having reference type

void reverseString(string &s, int iNode, int lNode){
    while(iNode < lNode){
        char temp = s[iNode];
        s[iNode] = s[lNode];
        s[lNode] = temp;
        iNode++;
        lNode--;
    }
}

The function could be defined simpler (without using standard features as for example std::swap) the following way

std::string & reverseString( std::string &s )
{
    for ( std::string::size_type i = 0, n = s.size(); i < n / 2; i++ )
    {
        char c = s[i];
        s[i] = s[n - i - 1];
        s[n - i - 1] = c;
    }

    return s;
}

And the function can be called like

cout << "String In Reverse Order: \n";
std::cout << reverseString( s ) << '\n';

Without using the loop you could define the function just the following way

std::string & reverseString( std::string &s )
{
    return s.assign( s.rbegin(), s.rend() );
}

As for your own function printString then it could be defined at least like

std::ostream & printString( const std::string &s, std::ostream &os = std::cout )
{
    for ( char c : s )
    {
        os << c;
    }

    return os;
}

and can be called like

printString( s ) << '\n';

How to write c++ code to reverse a string without using inbuilt function?

1 Answers1