convert a number from base 2 to base 8 in swift

To convert a number from base 2 to base 8 in Swift, we can follow these steps:

1. First, we need to convert the binary number to decimal.
2. Then, we can convert the decimal number to octal.

Here's the code to convert a binary number to octal in Swift:

main.swift
func binaryToOctal(binary: String) -> String {
    // Convert binary to decimal
    let decimal = Int(strtoul(binary, nil, 2))
    
    // Convert decimal to octal
    let octal = String(decimal, radix: 8)
    
    return octal
}
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In the above code, we first use strtoul function to convert the binary string to decimal. The strtoul function takes three arguments: the binary string, a pointer to an optional UnsafeMutablePointer<Int8> (which we pass as nil), and the base of the input number system (which is 2 for binary). This function returns an UInt32 value which we can safely convert to an Int.

Next, we use the String initializer that takes a decimal value and a radix (which is 8 for octal) and returns the octal string.

Here's an example of how to use the binaryToOctal function:

main.swift
let binary = "11001110"
let octal = binaryToOctal(binary: binary)
print(octal) // Output: 316
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In the above example, we convert the binary number "11001110" to octal and print the result which is "316".