STRINGS

In C, strings are arrays of characters terminated by a null character ('\0'). Strings are a common and essential feature in C programming for handling text data. Here’s an overview of working with strings in C:

Declaring and Initializing Strings

1. Declaration

You can declare a string using a character array or a pointer to a character.

char str1[20]; // Character array
char *str2;    // Pointer to a character

2. Initialization

Strings can be initialized during declaration.

char str1[20] = "Hello, World!";
char *str2 = "Hello, World!";

When a string is initialized with a double-quoted string literal, it automatically includes the null character at the end.

String Input and Output

1. Reading Strings

You can use scanf, gets, or fgets to read strings from input.

#include <stdio.h>
 
int main() {
    char str[50];
 
    // Using scanf
    printf("Enter a string: ");
    scanf("%s", str); // Note: scanf stops at whitespace
    printf("You entered: %s\n", str);
 
    // Using fgets
    printf("Enter another string: ");
    fgets(str, sizeof(str), stdin); // fgets includes whitespace and reads until newline
    printf("You entered: %s", str);
 
    return 0;
}

Important: gets is not recommended due to the risk of buffer overflow. Always use fgets for safer input handling.

2. Printing Strings

You can use printf to print strings.

#include <stdio.h>
 
int main() {
    char str[] = "Hello, World!";
    printf("%s\n", str);
 
    return 0;
}

String Functions

C provides several standard library functions for handling strings. These functions are declared in the string.h header file.

1. String Length

strlen calculates the length of a string (excluding the null character).

#include <stdio.h>
#include <string.h>
 
int main() {
    char str[] = "Hello, World!";
    printf("Length of string: %lu\n", strlen(str));
 
    return 0;
}

2. String Copy

strcpy copies one string to another.

#include <stdio.h>
#include <string.h>
 
int main() {
    char source[] = "Hello, World!";
    char destination[20];
 
    strcpy(destination, source);
    printf("Copied string: %s\n", destination);
 
    return 0;
}

3. String Concatenation

strcat appends one string to the end of another.

#include <stdio.h>
#include <string.h>
 
int main() {
    char str1[20] = "Hello";
    char str2[] = ", World!";
 
    strcat(str1, str2);
    printf("Concatenated string: %s\n", str1);
 
    return 0;
}

4. String Comparison

strcmp compares two strings lexicographically.

#include <stdio.h>
#include <string.h>
 
int main() {
    char str1[] = "Hello";
    char str2[] = "World";
 
    int result = strcmp(str1, str2);
    if (result == 0) {
        printf("Strings are equal.\n");
    } else if (result < 0) {
        printf("str1 is less than str2.\n");
    } else {
        printf("str1 is greater than str2.\n");
    }
 
    return 0;
}

5. String Searching

strstr finds the first occurrence of a substring in a string.

#include <stdio.h>
#include <string.h>
 
int main() {
    char str[] = "Hello, World!";
    char *substr = "World";
 
    char *result = strstr(str, substr);
    if (result) {
        printf("Substring found at position: %ld\n", result - str);
    } else {
        printf("Substring not found.\n");
    }
 
    return 0;
}

Manual String Manipulation

Sometimes you may need to manipulate strings manually. Here are a few examples:

1. Copying a String Manually

#include <stdio.h>
 
void stringCopy(char *destination, const char *source) {
    while (*source) {
        *destination = *source;
        destination++;
        source++;
    }
    *destination = '\0'; // Null-terminate the destination string
}
 
int main() {
    char source[] = "Hello, World!";
    char destination[20];
 
    stringCopy(destination, source);
    printf("Copied string: %s\n", destination);
 
    return 0;
}

2. Concatenating Strings Manually

#include <stdio.h>
 
void stringConcat(char *destination, const char *source) {
    while (*destination) {
        destination++; // Move to the end of the destination string
    }
    while (*source) {
        *destination = *source;
        destination++;
        source++;
    }
    *destination = '\0'; // Null-terminate the destination string
}
 
int main() {
    char str1[20] = "Hello";
    char str2[] = ", World!";
 
    stringConcat(str1, str2);
    printf("Concatenated string: %s\n", str1);
 
    return 0;
}