A Practical Guide to Copying and Concatenating Strings in C

In C, a string is essentially an array of characters, ending with a special null character (‘\0’) to indicate the end of the string.

C does not have a built-in string data type like other high-level languages, so strings are usually handled using character arrays.

Declaring and Initializing a String

A string can be declared as an array of characters or using a string literal.

1.  Using Character Array:

char str[20];  // Declare a string with a maximum size of 20 characters

2.  Using String Literal:

char str[] = “Hello, World!”;  // Automatically sizes the array based on the length of the string

String Operations

Some common string operations in C include:

1. String Length (strlen):

• • To find the length of a string (excluding the null terminator), you can use the strlen function.

#include <string.h>

size_t len = strlen(str);  // Returns the length of the string

2. Copying Strings (strcpy):

• • To copy one string into another, use strcpy.

char source[] = “Hello”;

char destination[20];

strcpy(destination, source);  // Copies “Hello” into destination

3. Concatenating Strings (strcat):

• • To append one string to another, use strcat.

char str1[30] = “Hello, “;

char str2[] = “World!”;

strcat(str1, str2);  // Appends “World!” to “Hello, “

4. Comparing Strings (strcmp):

• • To compare two strings lexicographically, use strcmp.

if (strcmp(str1, str2) == 0) {

    printf(“Strings are equal\n”);

} else {

    printf(“Strings are not equal\n”);

}

5. Copying a specified number of characters (strncpy):

• • If you want to copy only a certain number of characters, you can use strncpy.

strncpy(destination, source, 5);  // Copies the first 5 characters of ‘source’ to ‘destination’

6. Finding a Character (strchr):

• • To locate the first occurrence of a character in a string, use strchr.

char *ptr = strchr(str, ‘o’);  // Finds the first ‘o’ in the string

7. Tokenizing a String (strtok):

• • To break a string into tokens (substrings), use strtok.

char str[] = “apple,banana,cherry”;

char *token = strtok(str, “,”);

while (token != NULL) {

    printf(“%s\n”, token);

    token = strtok(NULL, “,”);

}

Example Code

Here’s a simple example of declaring, manipulating, and printing a string in C:

#include <stdio.h>

#include <string.h>

int main() {

    char greeting[] = “Hello, World!”;

    // Print the string

    printf(“Greeting: %s\n”, greeting);

    printf(“Length: %lu\n”, strlen(greeting));

    // Modify the string

    greeting[7] = ‘C’;

    printf(“Modified Greeting: %s\n”, greeting);

    return 0;

}

Important Notes:

• Null Terminator (‘\0’): Every string in C is terminated with a special character ‘\0’ to indicate the end of the string. This is why the length of a string is the number of characters before ‘\0’.
• Fixed Size: Strings in C have a fixed size when declared as character arrays, so you need to ensure the array is large enough to hold the string and its null terminator.