1, Design and implement a lexical analyzer using C language to recognize all valid tokens in the input program. The lexical analyzer should ignore redundant spaces, tabs and newlines. It should also ignore comments

#include <stdio.h>

#include <ctype.h>

int main() {

    char c;

    while ((c = getchar()) != EOF) {

        if (isspace(c)) {

            // Ignore whitespace, tabs, and newlines

            continue;

        }

        if (c == '/') {

            // Check for comments

            char nextChar = getchar();

            if (nextChar == '/') {

                while ((nextChar = getchar()) != '\n');

            } else {

                putchar(c);

                putchar(nextChar);

            }

        } else {

            putchar(c);

        }

    }

    return 0;

}

```

Now, let's explain each line of the code:

1. `#include <stdio.h>`: This includes the standard input/output library for input and output operations.

2. `#include <ctype.h>`: This includes the ctype library, which provides functions to classify and transform characters.

3. `int main() {`: The main function, where the program execution begins.

4. `char c;`: Declares a character variable `c` to hold the current character read from input.

5. `while ((c = getchar()) != EOF) {`: This starts a loop that reads characters from input until the end of the file (EOF) is reached.

6. `if (isspace(c)) {`: Checks if the current character is a whitespace character (space, tab, newline).

7. `continue;`: If the current character is a whitespace character, the loop continues to the next iteration, ignoring the whitespace.

8. `if (c == '/') {`: Checks if the current character is a slash.

9. `char nextChar = getchar();`: Reads the next character from input after the slash.

10. `if (nextChar == '/') {`: Checks if the next character is also a slash, indicating the start of a single-line comment.

11. `while ((nextChar = getchar()) != '\n');`: Skips characters until a newline is encountered, effectively ignoring the single-line comment.

12. `} else {`: If the next character is not a slash, this block handles other cases.

13. `putchar(c);`: Outputs the current character to the standard output.

14. `putchar(nextChar);`: Outputs the next character (after the slash) to the standard output.

15. `} else {`: If the current character is neither a whitespace nor a slash, this block handles other characters.

16. `putchar(c);`: Outputs the current character to the standard output.

17. `}`: Closes the inner `else` block.

18. `}`: Closes the loop.

19. `return 0;`: Exits the program with a success status.

This code reads characters from input, processes them according to the rules for ignoring whitespace and comments, and outputs valid tokens. Keep in mind that this is a basic example, and in real-world scenarios, lexical analyzers are more complex and capable of recognizing various token types and patterns.