23 Jan C Prog 1 SS

 

1. Header Files

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

• #include <stdio.h>: Includes the Standard Input/Output library to enable input/output operations like printf().
• #include <string.h>: Includes the String library to provide string manipulation functions like strlen(), strcpy(), strcat(), etc.

2. Main Function

int main() {

• The main() function is the entry point of the C program.

3. Declaring Strings

char str1[100] = "Hello, World!";
char str2[100] = "Welcome to C programming.";
char str3[100];
char str4[100] = "C is fun!";

• str1, str2, str4 are initialized with strings "Hello, World!", "Welcome to C programming.", and "C is fun!", respectively.
• str3 is declared as a character array but is not initialized at this point.

4. strlen - Find the Length of a String

printf("Length of str1: %zu\n", strlen(str1));
printf("Length of str2: %zu\n\n", strlen(str2));

• strlen(str1): The strlen() function returns the length of the string str1 (excluding the null-terminating character).
• It prints the length of str1 and str2 using the format specifier %zu for size_t, the return type of strlen().

5. strcpy - Copy One String Into Another

strcpy(str3, str1);
printf("After copying, str3: %s\n\n", str3);

• strcpy(str3, str1): Copies the contents of str1 into str3. After this, str3 will hold "Hello, World!".
• The printf() statement prints the copied string str3.

6. strcat - Concatenate Two Strings

strcat(str1, " ");
strcat(str1, str4);
printf("After concatenation, str1: %s\n\n", str1);

• strcat(str1, " "): Concatenates a space (" ") to the end of str1, changing it to "Hello, World! ".
• strcat(str1, str4): Then, concatenates str4 ("C is fun!") to str1, resulting in "Hello, World! C is fun!".
• The program prints the concatenated string.

7. strcmp - Compare Two Strings

int result = strcmp(str1, str2);
if (result == 0) {
    printf("str1 and str2 are equal.\n\n");
} else if (result > 0) {
    printf("str1 is greater than str2.\n\n");
} else {
    printf("str1 is less than str2.\n\n");
}

• strcmp(str1, str2): Compares str1 and str2 lexicographically. It returns:
  • 0 if the strings are equal,
  • a positive value if str1 is lexicographically greater than str2,
  • a negative value if str1 is lexicographically less than str2.
• The program checks the result and prints whether str1 and str2 are equal, or if one is greater or less than the other.

8. strchr - Find the First Occurrence of a Character

char *pos = strchr(str2, 'C');
if (pos) {
    printf("Character 'C' found in str2 at position: %ld\n\n", pos - str2);
} else {
    printf("Character 'C' not found in str2.\n\n");
}

• strchr(str2, 'C'): Searches for the first occurrence of the character 'C' in str2. If found, it returns a pointer to the character; otherwise, it returns NULL.
• The program calculates the position of 'C' in str2 by subtracting the base address of str2 from pos, and prints the position.

9. strstr - Find the First Occurrence of a Substring

char *subpos = strstr(str2, "programming");
if (subpos) {
    printf("Substring \"programming\" found at position: %ld\n\n", subpos - str2);
} else {
    printf("Substring \"programming\" not found.\n\n");
}

• strstr(str2, "programming"): Searches for the substring "programming" within str2. If found, it returns a pointer to the first occurrence of the substring.
• The position is calculated similarly as in the previous step, and the program prints the result.

10. memset - Fill Memory with a Constant Byte

memset(str3, '*', 5);
str3[5] = '\0'; // Null-terminate the string
printf("After memset, str3: %s\n\n", str3);

• memset(str3, '*', 5): Fills the first 5 bytes of str3 with the character '*'. After this, str3 becomes "*****".
• The null terminator \0 is manually added at position 5 to ensure the string is properly terminated.
• The program prints the modified string str3.

11. strncpy - Copy a Specific Number of Characters

strncpy(str3, str2, 7);
str3[7] = '\0'; // Null-terminate the string
printf("After strncpy, str3: %s\n\n", str3);

• strncpy(str3, str2, 7): Copies the first 7 characters from str2 into str3. After this, str3 will contain "Welcome".
• A null terminator is manually added at position 7.
• The program prints the copied string str3.

12. strtok - Tokenize a String

char str5[100] = "Tokenize this string into words.";
char *token = strtok(str5, " ");
printf("Tokens:\n");
while (token) {
    printf("%s\n", token);
    token = strtok(NULL, " ");
}

• strtok(str5, " "): The strtok() function splits the string str5 into tokens based on the delimiter " " (space in this case). It returns a pointer to the first token.
• The while loop continues calling strtok() with NULL as the first argument to tokenize the remaining parts of the string.
• Each token is printed on a new line.

13. Return Statement

return 0;

• The main() function returns 0 to indicate that the program has executed successfully.

14. Program End

}

• Marks the end of the main() function.