C Exercises: Copy One string to another

C Recursion : Exercise-19 with Solution

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:

C Programming Code Editor:

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