Codes

1. Multiples of 3 or 7

Change the logic to print numbers that are multiples of 3 or 7 instead of 5 or 6.

// Inside process_file, replace the if condition:
if (val != 0 && (val % 3 == 0 || val % 7 == 0)) {
    printf("%d\n", val);
}

2. Multiples of 30 (5 AND 6)

Modify the program to only print numbers that are both multiples of 5 AND 6.

// Inside process_file:
if (val != 0 && (val % 5 == 0 && val % 6 == 0)) {
    printf("%d\n", val);
}

3. Custom Separators

Update the separator string to include custom characters like @, #, or $.

// Inside process_file:
char *separators = " -\r\t\n./,@#$";

4. Match Counter

Instead of printing the numbers, print the total count of how many matches were found in the file.

// 1. Change process_file to return the count of matches
int process_file(int fd) {
    int count = 0;
    // ... inside loop when a match is found:
    if (val != 0 && (val % 5 == 0 || val % 6 == 0)) {
        count++;
    }
    // ... repeat in EOF fix
    return count;
}

// 2. In main(), accumulate the result:
int total_matches = 0;
for (int i = 1; i < argc; i++) {
    // ... open file ...
    total_matches += process_file(fd);
}
printf("Total matches: %d\n", total_matches);

5. Standard Input Support

Modify sixfive to read from standard input (0) if no filename argument is provided.

int main(int argc, char *argv[]) {
  if (argc < 2) {
    process_file(0); // Read from stdin (file descriptor 0)
    exit(0);
  }

  for (int i = 1; i < argc; i++) {
    int fd = open(argv[i], O_RDONLY);
    if (fd >= 0) {
      process_file(fd);
      close(fd);
    }
  }
  exit(0);
}

6. Range Filter (10-100)

Implement a range filter to only print matching numbers that fall between 10 and 100.

// Inside process_file:
if (val != 0 && (val % 5 == 0 || val % 6 == 0) && (val >= 10 && val <= 100)) {
    printf("%d\n", val);
}

7. Hexadecimal Output

Change the output format to print all identified numbers in hexadecimal.

// Inside process_file:
if (val != 0 && (val % 5 == 0 || val % 6 == 0)) {
    printf("0x%x\n", val); // %x prints in hex
}

8. Exclude Number 6

Modify the code so that it never prints the number 6, even if it is a multiple of 6.

// Inside process_file:
if (val != 0 && (val % 5 == 0 || val % 6 == 0) && val != 6) {
    printf("%d\n", val);
}

9. Sum Summary

Add a summary at the end of the output that prints the total sum of all numbers found.

// In main():
int total_sum = 0;

// Update process_file to return the sum of matches in that file:
int process_file(int fd) {
    int file_sum = 0;
    // ... inside loop ...
    if (val != 0 && (val % 5 == 0 || val % 6 == 0)) {
        file_sum += val;
    }
    return file_sum;
}

// In main() after the loop:
printf("Sum: %d\n", total_sum);

10. Filename Header

Update the program to print the filename on the first line before listing the numbers found.

// Inside main() for loop:
for (int i = 1; i < argc; i++) {
    int fd = open(argv[i], O_RDONLY);
    if (fd >= 0) {
        printf("File: %s\n", argv[i]); // Print header here
        process_file(fd);
        close(fd);
    }
}