C Exercises: Copy One string to another

Last update on March 20 2025 12:37:47 (UTC/GMT +8 hours)

19. String Copy Recursion Variants

Write a program in C to copy one string to another using recursion.

Pictorial Presentation:

Sample Solution:

C Code:

#include <stdio.h>
 
void copyString(char [], char [], int);
 
int main()
{
    char stng1[20], stng2[20];
    printf("\n\n Recursion : Copy One string to another :\n");
	printf("---------------------------------------------\n"); 	
 
    printf(" Input the  string to copy : ");
    scanf("%s", stng1);
    copyString(stng1, stng2, 0);
    printf("\n The string successfully copied.\n\n");
    printf(" The first string is : %s\n", stng1);
    printf(" The copied string is : %s\n\n", stng2);
    return 0;
}
 
void copyString(char stng1[], char stng2[], int ctr)
{
    stng2[ctr] = stng1[ctr];
    if (stng1[ctr] == '\0')
        return;
    copyString(stng1, stng2, ctr + 1);
}

Sample Output:

 Recursion : Copy One string to another :                                                                     
---------------------------------------------                                                                 
 Input the  string to copy : w3resource                                                                       
                                                                                                              
 The string successfully copied.                                                                              
                                                                                                              
 The first string is : w3resource                                                                             
 The copied string is : w3resource

Explanation:

void copyString(char stng1[], char stng2[], int ctr)
{
    stng2[ctr] = stng1[ctr];
    if (stng1[ctr] == '\0')
        return;
    copyString(stng1, stng2, ctr + 1);
}

The copyString() function takes two character arrays stng1 and stng2 and an integer ctr as arguments. It recursively copies the characters of stng1 to stng2 starting from index ctr until it finds a null character (\0) in stng1. At that point, it returns from the function.

The character at index ctr of stng1 is copied to the corresponding index of stng2.
If the character at index ctr of stng1 is null (\0), the function returns.
Otherwise, the function calls itself with ctr+1 as the new index.
The function continues to copy the characters until it reaches the end of stng1.

Time complexity and space complexity:

The time complexity of this function is O(n) where n is the length of the input string stng1.

The space complexity is O(n) as well since the function uses recursion to copy the string, which creates a new stack frame for each recursive call.

Flowchart:

For more Practice: Solve these Related Problems:

Write a C program to copy a string and convert it to uppercase recursively.
Write a C program to copy a string in reverse order using recursion.
Write a C program to recursively copy a string to a new buffer and count the number of characters copied.
Write a C program to copy a string while removing all vowels using recursion.

C Programming Code Editor:

Previous: Write a program in C to find the Hailstone Sequence of a given number upto 1.
Next: Write a program in C to find the first capital letter in a string using recursion.