Streams

You have been using the stdio.h for nearly every lab, and will use it for nearly every program you will ever create in C.

Standard Input and Output enables the program to take inputs and produce outputs. These two categories are broken numerically as:

• Standard In is numerically defined as 0

• Standard Out is numerically dedined as 1

• Standard Error is numerically defined as 2

C Task 1: Starting out...

1. Create a new directory called Streams, name the child file inside the Streams directory streams.c

2. Define two variables both integers called number and result.

3. Prompt the user to enter a number using the standard out function printf()

4. Next using standard in's scanf() read in the users input use the format specifier %d and save it to &number

5. Add some conditional checking to compare the number to the value 2, where the comparison is number does not equal 2.

6. Inside the conditonal block use the perror function to with the string "Error reading input", on the next line use return 1 to indicate an error using the exit code 1.

7. Outside of the conditonal block multiply the number by itself and assign the result to result,

8. Finally, print the result using printf("The square of %d is: %d\n", number, result);

   Suppressed Code... [27 lines]

   #include <stdio.h>
   
   int main() {
       // Declare variables for input and result
       int number;
       int result;
   
       // Prompt the user for input
       printf("Enter a number: ");
   
       // Read user input
       scanf("%d", &number)
   
       // compare user inputted value
       if ( number != 2) {
           // Handle input error using perror()
           perror("Error reading input");
           return 1; // Exit with an error code
       }
   
       // Perform a simple calculation (for example, squaring the input)
       result = number * number;
   
       // Display the result
       printf("The square of %d is: %d\n", number, result);
   
       return 0; // Exit successfully
   }
   

9. Run the code and when prompted enter the any number that is not 2.

   Output

   • Notice how the terminal has rendered the error message, this is because error, 2 stream is different to standard out, 1, stream

10. Run a second time and then enter the value 2

C Task 2: Read and Write a File

The program you will write assumes that there is an input file named input.txt that stores two integers. The program will then create an output file named output.txt with the multiplication result of those two numbers. Error handling is incorporated using perror() for file-related errors.

1. Prepare Input File

Create a new file and places in the resources folder of the solution view, call it input.txt, inside the file input two numbers seperated by space that range from 0 to 50000, save the file.

2. Define Main Function

Now modify main(), by placing using the FILE *inputFile, *outputFile; at the top of main().

3. Initialise Variables

On the next line define three integer variables called, numOne, numTwo and result:

int num1, num2, result;

4. Open Input File

Create two newlines and the second one you need to reproduce the follwoing:

// Open input file for reading
inputFile = fopen("input.txt", "r");
if (inputFile == NULL) {
    perror("Error opening input file");
    return 1; // Exit with an error code
}

5. Validating Input File

If inputFile is not NULL then the following code would excute, input the following:

// Read two integers from the input file
if (fscanf(inputFile, "%d %d", &numOne, &numTwo) != 2) {
    // Handle input error using perror()
    perror("Error reading input from file");
    fclose(inputFile); // Close the input file
    return 1; // Exit with an error code
}

6. Perform Multiplication

The calculation can now be performed, multiply numOne by numTwo and store in result

fclose(inputFile); // Close the input file

// Perform multiplication
result = numOne * numTwo;

7. Write to Output File

In a similar fashion to the inputFile we need to write to a new file, reproduce the following:

// Open output file for writing
outputFile = fopen("output.txt", "w");
if (outputFile == NULL) {
    perror("Error opening output file");
    return 1; // Exit with an error code
}

5. Validating Output File

Again, repeating the structure of step 5, we can write to the file the result variable. Reproduce the following:

// Write the result to the output file
if (fprintf(outputFile, "Multiplication result: %d\n", result) < 0) {
    // Handle output error using perror()
    perror("Error writing output to file");
    fclose(outputFile); // Close the output file before exiting
    return 1; // Exit with an error code
}

7. Print Success Message

On success the file needs to be close so after the if(..){..} add fclose("outputFile) and on a new line printf("Operation completed successfully.\n");

fclose("outputFile);
printf("Operation completed successfully.\n");

8. Run the Program

Compile and run the code.

9. Verify the Output

Open the output.txt file to see the result of the multiplication.

C Full code

#include <stdio.h>

int main() {
    FILE *inputFile, *outputFile;
    int numOne, numTwo, result;

    // Open input file for reading
    inputFile = fopen("input.txt", "r");
    if (inputFile == NULL) {
        perror("Error opening input file");
        return 1; // Exit with an error code
    }

    // Read two integers from the input file
    if (fscanf(inputFile, "%d %d", &numOne, &numTwo) != 2) {
        // Handle input error using perror()
        perror("Error reading input from file");
        fclose(inputFile); // Close the input file
        return 1; // Exit with an error code
    }

    fclose(inputFile); // Close the input file

    // Perform multiplication
    result = numOne * numTwo;

     // Open output file for writing
    outputFile = fopen("output.txt", "w");
    if (outputFile == NULL) {
        perror("Error opening output file");
        return 1; // Exit with an error code
    }

    // Write the result to the output file
    if (fprintf(outputFile, "Multiplication result: %d\n", result) < 0) {
        // Handle output error using perror()
        perror("Error writing output to file");
        fclose(outputFile); // Close the output file before exiting
        return 1; // Exit with an error code
    }

    fclose(outputFile); // Close outputFile file2

    printf("Operation completed successfully.\n");

    return 0; // Exit successfully
}

Python Task 1: Starting out...

1. Create a new file called streams.py

2. At the top of the file put import sys package

3. Next you need to create a try:-except: block

4. Inside try: create a variable called user_input and assign to it the output of the following function input("Enter a number: ")

5. Next convert the user_input to a float using the float(...) function, assign this to number

6. On the next line square the number... and assign it to result

7. Now you we need to output the result to the user. Use print(f"") notation

   try code... [14 lines]

   import sys  # Import for handling exit
   
   try:
       # Prompt the user to enter a number
       user_input = input("Enter a number: ")
   
       # Convert the input to a float
       number = float(user_input)
   
       # Perform the calculation (square the number)
       result = number ** 2
   
       # Display the result
       print(f"The square of {number} is {result}")
   

8. Next we need to add the except: incase there was an error inside try:

9. Using print() return an appropriate error message

10. Finally, use the sys package and use the module exit(1)

    Full code... [18 lines]

    import sys # Import for handling exit

    try: # Prompt the user to enter a number user_input = input("Enter a number: ")

    # Convert the input to a float
    number = float(user_input)
    
    # Perform the calculation (square the number)
    result = number ** 2
    
    # Display the result
    print(f"The square of {number} is {result}")
    

    except ValueError: # Handle invalid input print("Error: Invalid input. Please enter a valid number.") sys.exit(1) # Exit the program with an error code

    
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11. Run the code and supply and numerical value, and then again with an alpha symbol.

Python Task 2: Read and Write a File

This lab assumes an input file named input.txt containing two integers. The program will create an output file named output.txt to store the multiplication result of those integers. Proper error handling is implemented for file-related issues.

1. Define Main Function

1. Create a new file called read_write.py

2. Begin by defining a main() function in Python.

import sys

def main():

2. Initialise Variables

Define variables to hold the two numbers and the result of their multiplication.

num_one = 0
num_two = 0
result = 0

3. Open Input File

Use a try...except block to handle potential errors when opening the file.

try:
    with open("input.txt", "r") as input_file:
        # Read two integers from the file
        try:
            num_one, num_two = map(int, input_file.read().split())
        except ValueError:
            print("Error: Could not read two integers from input file.", file=sys.stderr)
            return
except FileNotFoundError:
    print("Error: Input file not found.", file=sys.stderr)
    return
except IOError as e:
    print(f"Error opening input file: {e}", file=sys.stderr)
    return

4. Perform Multiplication

Multiply the two numbers and store the result.

result = num_one * num_two

5. Write to Output File

Use another try...except block to handle potential issues when writing to the output file.

try:
    with open("output.txt", "w") as output_file:
        # Write the result to the output file
        output_file.write(f"Multiplication result: {result}\n")
except IOError as e:
    print(f"Error writing to output file: {e}", file=sys.stderr)
    return

6. Print Success Message

Inform the user that the operation completed successfully.

    print("Operation completed successfully.")

7. Run the Program

Call the main() function to execute the code.

if __name__ == "__main__":
    main()

8. Verify the Output

1. Run the program.
2. Open output.txt to verify that it contains the correct multiplication result.

9. Full Code here

import sys

def main():
    num_one = 0
    num_two = 0
    result = 0

    try:
        with open("input.txt", "r") as input_file:
            # Read two integers from the file
            try:
                num_one, num_two = map(int, input_file.read().split())
            except ValueError:
                print("Error: Could not read two integers from input file.", file=sys.stderr)
                return
    except FileNotFoundError:
        print("Error: Input file not found.", file=sys.stderr)
        return
    except IOError as e:
        print(f"Error opening input file: {e}", file=sys.stderr)
        return

    result = num_one * num_two

    try:
        with open("output.txt", "w") as output_file:
            # Write the result to the output file
            output_file.write(f"Multiplication result: {result}\n")
    except IOError as e:
        print(f"Error writing to output file: {e}", file=sys.stderr)
        return
    
    print("Operation completed successfully.")

if __name__ == "__main__":
    main()