To find the sum of all numbers in an array in C, you can use a loop to iterate through each element of the array and add it to a variable that keeps track of the sum. Here's an example:

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#include <stdio.h>

int main() {
    int numbers[] = {2, 4, 6, 8, 10};
    int size = sizeof(numbers) / sizeof(numbers[0]);
    int sum = 0;

    for (int i = 0; i < size; i++) {
        sum += numbers[i];
    }

    printf("The sum is: %d\n", sum);

    return 0;
}

In this example, we have an array of numbers {2, 4, 6, 8, 10}. The size variable is determined by dividing the total size of the array by the size of its first element. Then, we use a for loop to iterate through each element of the array and add it to the sum variable. Finally, we print the sum.

Output:

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The sum is: 30

To write a UNIX command line interpreter (shell) in C, you can follow these general steps:

1. Read input from the user using the fgets function, which reads input from the standard input stream (stdin) until a newline character is encountered.
2. Tokenize the input into commands and arguments using the strtok function.
3. Use system calls such as fork, execve, and waitpid to create child processes and run the commands entered by the user.
4. Implement built-in shell commands such as cd, exit, and history using appropriate system calls.

Here's a simple example of how to write a command line interpreter in C:

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#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/wait.h>

#define MAX_LINE_LENGTH 80
#define MAX_ARGS 10

int main() {
    char line[MAX_LINE_LENGTH];
    char* args[MAX_ARGS];
    int status;

    while (1) {
        printf("shell> ");
        fgets(line, MAX_LINE_LENGTH, stdin);

        // tokenize the input
        int i = 0;
        args[i] = strtok(line, " \n");
        while (args[i] != NULL) {
            i++;
            args[i] = strtok(NULL, " \n");
        }
        args[i] = NULL;

        // handle built-in commands
        if (strcmp(args[0], "cd") == 0) {
            chdir(args[1]);
            continue;
        }
        else if (strcmp(args[0], "exit") == 0) {
            exit(0);
        }

        // create a child process and execute the command
        pid_t pid = fork();
        if (pid < 0) {
            perror("fork failed");
            exit(1);
        }
        else if (pid == 0) {
            // child process
            execvp(args[0], args);
            perror("execvp failed");
            exit(1);
        }
        else {
            // parent process
            waitpid(pid, &status, 0);
        }
    }
    return 0;
}

This is just a simple example and there are many more features you can add to a shell, such as input/output redirection, piping, and background processes. For more information, you can read the following resources:

• Write a Shell in C
• Unix Shell Programming

To check if a number is odd in C, we can use the modulus operator %.

Here's an example:

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int num = 5;

if(num % 2 == 1){
  printf("The number is odd");
}
else{
  printf("The number is even");
}

In this example, we use the modulus operator to get the remainder of num / 2. If the remainder is 1, then the number is odd. If the remainder is 0, then the number is even.