1. Make a C program that will input two integers and then to enter an option as follows:

• 1 = to add the two integers.
• 2 = to subtract the second integer from the first.
• 3 = to multiply the integers
• 4 = to divide the first integer by the second integer.
Display an error message if the user enters an option other than 1 through 4 or if the user chooses the divide option by enters 0 for the second integer. Print the results of the arithmetic.T The filename will be Calculate.c
2. Modify the previous program. If the chosen option is 2, the two integers must be compared before the arithmetic operation. Subtract the two integers provided the first integer is greater than the second integer, otherwise add the two integers and subtract the second integer from the first integer.

To create a C program that fulfills the given requirements, follow these steps:

1. Open a text editor and create a new file. Save it with the name "Calculate.c." This will be the file where we write our C program.

2. Start the program by including the necessary header files:
```c
#include <stdio.h>
```

3. Declare the main function and define the variables needed:
```c
int main() {
int num1, num2, option, result;

// Prompt the user to input two integers and the option
printf("Enter two integers: ");
scanf("%d %d", &num1, &num2);
printf("Enter an option (1-4): ");
scanf("%d", &option);
}
```

4. Use conditionals (if-else statements) to implement the selected option and perform the arithmetic operations:
```c
if (option == 1) {
result = num1 + num2;
printf("Addition: %d\n", result);
}
else if (option == 2) {
if (num1 > num2) {
result = num1 - num2;
printf("Subtraction: %d\n", result);
} else {
result = num1 + num2 - num2;
printf("Addition and subtraction: %d\n", result);
}
}
else if (option == 3) {
result = num1 * num2;
printf("Multiplication: %d\n", result);
}
else if (option == 4) {
if (num2 != 0) {
result = num1 / num2;
printf("Division: %d\n", result);
} else {
printf("Error: Cannot divide by zero.\n");
}
}
else {
printf("Error: Invalid option.\n");
}
```

5. Finally, close the main function:
```c
return 0;
```

The completed program should look like this:

```c
#include <stdio.h>

int main() {
int num1, num2, option, result;

printf("Enter two integers: ");
scanf("%d %d", &num1, &num2);
printf("Enter an option (1-4): ");
scanf("%d", &option);

if (option == 1) {
result = num1 + num2;
printf("Addition: %d\n", result);
}
else if (option == 2) {
if (num1 > num2) {
result = num1 - num2;
printf("Subtraction: %d\n", result);
} else {
result = num1 + num2 - num2;
printf("Addition and subtraction: %d\n", result);
}
}
else if (option == 3) {
result = num1 * num2;
printf("Multiplication: %d\n", result);
}
else if (option == 4) {
if (num2 != 0) {
result = num1 / num2;
printf("Division: %d\n", result);
} else {
printf("Error: Cannot divide by zero.\n");
}
}
else {
printf("Error: Invalid option.\n");
}

return 0;
}
```

To compile and run the program, you will need a C compiler. Follow these steps:

1. Open the command prompt or terminal.

2. Navigate to the directory where you saved the "Calculate.c" file using the `cd` command.

3. Compile the program using the command: `gcc Calculate.c -o Calculate`

4. Run the program by executing: `./Calculate`

5. Follow the prompts to input the two integers and choose an option. The program will display the result based on the selected option.

By modifying the program to compare the two integers for the subtraction option, the updated code should look like this:

```c
#include <stdio.h>

int main() {
int num1, num2, option, result;

printf("Enter two integers: ");
scanf("%d %d", &num1, &num2);
printf("Enter an option (1-4): ");
scanf("%d", &option);

if (option == 1) {
result = num1 + num2;
printf("Addition: %d\n", result);
}
else if (option == 2) {
if (num1 > num2) {
result = num1 - num2;
printf("Subtraction: %d\n", result);
} else {
result = num1 + num2;
printf("Addition: %d\n", result);
result = num1 - num2;
printf("Subtraction: %d\n", result);
}
}
else if (option == 3) {
result = num1 * num2;
printf("Multiplication: %d\n", result);
}
else if (option == 4) {
if (num2 != 0) {
result = num1 / num2;
printf("Division: %d\n", result);
} else {
printf("Error: Cannot divide by zero.\n");
}
}
else {
printf("Error: Invalid option.\n");
}

return 0;
}
```

Now, when the option 2 is chosen, the program compares the two integers. If the first integer is greater than the second, it performs subtraction. Otherwise, it performs addition and then subtraction.