C Program to Copy a String

  • Write a C program to copy string.
  • Write a C program to create a duplicate string.

We first take a string as input from user using gets function and store it in a character array. Now, we have to copy all characters of input string to another string including null character. At last we have to print input string as well as copy string on screen. We can either use strcpy function of string.h header file to copy string or write our own function to copy string using pointers.

C program to copy a string using strcpy function

To use strcpy function, we must include string.h header file in our program. Here is the declaration for strcpy() function.


char *strcpy(char *destination, const char *source);
  • source is the pointer to the string to be copied.
  • destination is the pointer to the string where the content is to be copied.
It returns a pointer to the copy string destination.

The strcpy() function copies the characters of source string into destination string, including null character. source must be a char pointer to a string terminated by a null character. After copying, it returns a pointer to destination.

/*
* C Program to copy a string using strcpy function
*/
#include <stdio.h>
#include <conio.h>
#include <string.h>

int main(){
    char inputString[100], copyString[100];
    printf("Enter a string of length less than 100 \n");
    gets(inputString);
    /*
     * char *strcpy(char *destination, const char *source)
     * Copies source into destination
     */
    strcpy(copyString, inputString);
    
    printf("Input String: %s \n", inputString);
    printf("Copy String: %s", copyString);
    
    getch();
    return 0;
}
Program Output
Enter a string of length less than 100 
Tech Crash Course
Input String: Tech Crash Course
Copy String: Tech Crash Course

Write a program in c to copy string using pointers in a user defined function

In this program, we are using our own function stringCopy to copy string. It takes source and destination pointers as parameters and does input validation(neither source nor destination pointer should be NULL). Inside while loop, it copies characters one by one from source string to destination string till null character. After copying it returns a pointer to destination string.

/*
* C Program to copy a string using a user defined function 
*/
#include <stdio.h>
#include <conio.h>
#include <string.h>

char* stringCopy(char *destination, char *source);
int main(){
    char inputString[100], copyString[100];
    printf("Enter a string of length less than 100 \n");
    gets(inputString);
    
    stringCopy(copyString, inputString);
    
    printf("Input String: %s \n", inputString);
    printf("Copy String: %s", copyString);
    
    getch();
    return 0;
}

/*
 * This function copy source String into destination String
 */
char* stringCopy(char *destination, char *source){
    int index = 0;
    if(NULL == source || NULL == destination){
        return NULL;
    }
    while(source[index] != '\0'){
        destination[index] = source[index];
        index++;
    }
    destination[index] = '\0';
    return destination;
}
Program Output
Enter a string of length less than 100 
techcrashcourse.com
Input String: techcrashcourse.com
Copy String: techcrashcourse.com

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