Reversing a String in C++ Using recursion
We used recursive functions to reverse a string from the below programs by using different conditions through if statements.
Implementation in C++
#include <bits/stdc++.h>
using namespace std;
/* Function to print reverse of the passed string */
void reverse(string str)
{
if(str.size() == 0)
{
return;
}
reverse(str.substr(1));
cout << str[0];
}
int main()
{
string a = "CodingNinjas";
reverse(a);
return 0;
}
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Output:
sajniNgnidoC
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Reversing a String in C++ Using Stack
In the below code, we are using a stack to reverse the string in C++.
Implementation in C++
// C++ program to reverse a string using stack
#include <bits/stdc++.h>
using namespace std;
// A structure to represent a stack
class Stack
{
public:
int top;
unsigned capacity;
char* array;
};
// function to create a stack of given
// capacity. It initializes size of stack as 0
Stack* createStack(unsigned capacity)
{
Stack* stack = new Stack();
stack->capacity = capacity;
stack->top = -1;
stack->array = new char[(stack->capacity * sizeof(char))];
return stack;
}
// Stack is full when top is equal to the last index
int isFull(Stack* stack)
{ return stack->top == stack->capacity - 1; }
// Stack is empty when top is equal to -1
int isEmpty(Stack* stack)
{ return stack->top == -1; }
// Function to add an item to stack.
// It increases top by 1
void push(Stack* stack, char item)
{
if (isFull(stack))
return;
stack->array[++stack->top] = item;
}
// Function to remove an item from the stack.
// It decreases top by 1
char pop(Stack* stack)
{
if (isEmpty(stack))
return -1;
return stack->array[stack->top--];
}
// A stack based function to reverse a string
void reverse(char str[])
{
// Create a stack of capacity
//equal to length of string
int n = strlen(str);
Stack* stack = createStack(n);
// Push all characters of string to stack
int i;
for (i = 0; i < n; i++)
push(stack, str[i]);
// Pop all characters of string and
// put them back to str
for (i = 0; i < n; i++)
str[i] = pop(stack);
}
int main()
{
char str[] = "CodingNinajs";
reverse(str);
cout << "The reversed string is " << str;
return 0;
}
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Output:
The reversed string is sjaniNgnidoC
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Reversing a String in C++ Using Inbuilt functions
The reverse() function directly reverses the given string, and this function is present in string.h library. The code for this function is inbuilt in the library, we need to just give a string as the input to the function.
Implementation in C++
// using reverse()
#include <bits/stdc++.h>
using namespace std;
int main()
{
string str = "CodingNinjas";
// Reverse str[begin..end]
reverse(str.begin(), str.end());
cout << str;
return 0;
}
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Output:
sajniNgnidoC
You can also try this code with Online C++ Compiler
Reversing a String in C++ Using another String/ Temporary Character
The idea is to transfer the string to another string in a reverse manner. All we need is the size of the string. The approach is to initialize a character array of the same size and start copying the elements of the input string from the end.
Implementation in C++
#include<iostream>
#include<stdio.h>
using namespace std;
int main()
{
char str[200], strTemp[200];
int len, i=0;
cout<<"Enter the String: ";
gets(str);
while(str[i]!='\0')
i++;
len = i;
strTemp[len] = '\0';
len--;
i = 0;
while(str[i]!='\0')
{
strTemp[len] = str[i];
i++;
len--;
}
i=0;
while(strTemp[i]!='\0')
{
str[i] = strTemp[i];
i++;
}
cout<<"\nReverse = "<<str;
cout<<endl;
return 0;
}
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Input:
CodingNinjas
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Output:
Reverse = sajniNgnidoC
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Reversing a String in C++ Using Constructor
In the below code, passing reverse iterators to the constructor returns us a reversed string.
Implementation in C++
// A simple C++ program to reverse string using constructor
#include <bits/stdc++.h>
using namespace std;
int main(){
string str = "CodingNinjas";
//Use of reverse iterators
string rev = string(str.rbegin(),str.rend());
cout<<rev<<endl;
return 0;
}
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Output:
sajniNgnidoC
You can also try this code with Online C++ Compiler
Frequently Asked Questions
How do you reverse a string?
Reversing a string can be done in multiple ways. Some of them are using the reverse() function, using constructor, recursion, and stack.
Which inbuilt function is used to reverse a string in C++?
The “reverse()” function is used to reverse a string in C++. It is present in string.h library.
How do you reverse a string without a reverse function?
To reverse a string, there are many methods like recursion, stacks, constructors in different languages.
Why the string is immutable?
The String itself is immutable in Java. The reason for this is that the = operator for strings is overloaded, takes the string literal as an argument, and then loops through the string literal copying each character into a mutable char array.
Conclusion
In this article, we discussed a basic operation of a string which is reversing a string in C++. We learned about many different methods to do this like using the reverse() function and stack and some of the programs using recursion, constructors in C++, and finally Stack using different strings and characters to reverse the string.
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