How to Append a Character to a String in C?

How to Append a Character to a String in C?

Last Updated : 05 Dec, 2024

In this article, we will learn how to append a character to a string using the C program.

The most straightforward method to append a character to a string is by using a loop traverse to the end of the string and append the new character manually.

C

#include <stdio.h>

void addChar(char *s, char c) {

  	// Move pointer to the end
    while (*s++);
  
    // Append the new character
    *(s - 1) = c;
  
    // Add null terminator to mark new end
    *s = '\0';
}

int main() {
    char s[20] = "Hello";
  	char c = '!';
    
    // Append '!' to the string
    addChar(s, c);
  
    printf("%s", s);
    return 0;
}

Output

Hello!

There are also a few other methods in C to append a character to a string. Some of them are as follows:

Table of Content

Using strlen()
Using memcpy()
Using strncat()

Using strlen()

The strlen() function returns the length of a string. The position where the new character should be appended can be directly accessed by finding the string’s current length. Add the character and then mark the new end.

C

#include <stdio.h>
#include <string.h>

void addChar(char *s, char c) {
  
    // Get the current length of the string
    int l = strlen(s);  
  
    // Add the new character at the end
    s[l] = c;
  
    // Add the null terminator
    s[l + 1] = '\0';
}

int main() {
    char s[20] = "Hello";
  	char c = '!';
    
    // Append '!' to the string
    addChar(s, c);
  
    printf("%s", s);
    return 0;
}

Output

Hello!

Using memcpy()

memcpy() is a function in the C standard library that copies a block of memory from one location to another. It can be used to copy the character declared as string at the end of the given string.

C

#include <stdio.h>
#include <string.h>

int main() {
    char s[20] = "Hello";
    char c[] = "!";

    // Copy c to the end of s + 1 to copy
  	// null terminator
    memcpy(s + strlen(s), c, strlen(c) + 1);  

    printf("%s", s);
    return 0;
}

Output

Hello!

memcpy() is overkill for appending a single character, as it is meant to work with blocks of memory and not just single elements like characters.

Using strncat()

In C, strncat() function is used to concatenate n number of characters form the second string to the first string. We can also use this function to append the given character to a string by declaring that character as a single character string.

C

#include <stdio.h>
#include <string.h>

int main() {
    char s[20] = "Hello";
    char c = '!';

    // Convert the character to a string and append it
    // Append the character '!' to the string
    strncat(s, &c, 1);  

    printf("%s", s);
    return 0;
}

Output

Hello!

How to Append a Character to a String in C?

C

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