C Program To Write A String Copy Function

This program copy text from one string to another string character-by-character with the help of string copy function. C programming language does have a builtin string copy function called strcpy() located in String.h header file.

In this example, you will write a program that uses a user-defined string copy function and does not use the builtin function.

This program is written using Dev-C++ compiler installed on a Windows 7 64-bit machine. If you want to use a different compiler, then modify the program source code to get an error-free program.

Also, before you begin, learn following C programming concepts if unfamiliar with them.

• C Reading Input Values.
• C Assignment Operators.
• C While Loop.
• C Arrays
• C Functions

Problem Definition

The program reads a string and then copy that string to another string and display the results.Each string is an array of characters with a null character at the end of the string. Make sure that the size of the string is same or greater than string 2 size, otherwise, there will be problem copying string 1 to string 2.

Start copying string character by character from string 1 to string 2, until we reach a null character.

Assign a null character to the string 2 when all characters of string 1 are copied successfully. This is because every string in C language must end with a ‘\0’.

For Example:-

Suppose the program reads “hello” to string 1, and then the starts copying string 1 to string 2 one character at a time until a null is encountered. See figure below.

Flowchart – String Copy Function

Program Code – String Copy Function

#include <stdio.h>
#include <string.h>
#include <conio.h>
int main ()
{
    char s1 [10];
    char s2 [10];
    int i;
    void strcopy (char s2 [10], char s1 [10]);
    /* Read the String 1 */
    printf ("Enter String 1 :");
    gets (s1);
    /* Copy the String 1 to String 2 */
    strcopy (s2, s1);
    /* Print both the functions */
        for (i=0; i<35; i++)
    printf("_");printf("\n\n");
    printf("String2=%s \n\nString1=%s\n",s2,s1);
    for(i=0;i<35;i++)
    printf("_");printf("\n\n");
    system("PAUSE");
    return 0;
}
void strcopy (char s2[10], char s1[10])
{
    int i= 0;
    while(s1[i] !='\0')
    {
        s2[i] = s1[i];
        ++i;
    }
    s2[i]='\0';
}

Output

Enter String 1:Hello world
__________________________________________
String2=Hello world

String1=Hello world
__________________________________________