Xen / coding-class v0.1.0-demo.2

Data types and conversions · Coding Class

Apply the chapter in three steps: an exercise, a program project, and a debugging task. Implement first, then consult the hints and completion criteria. Use a separate file or working directory for each task.

1. Exercise · Compare division results

Print 5 / 2, float(5 / 2), and float(5) / 2.0 in order and explain the difference.

Completion: Output is 2, 2.0, and 2.5.

Hint: Find the point where the fractional part is discarded.

2. Build a program · Calculate an average

Print the floating-point average of scores 7, 8, and 10. Store an integer total, then convert before division. Also check scores 0, 0, and 0.

Completion: The averages are approximately 8.333333 and 0.0. Do not first truncate the result to integer 8.

Hint: Use float(total) / 3.0.

3. Debug · Fix a numeric mismatch

Fix the program below while keeping count typed as I32. Explain whether the same fix always works for values outside the I32 range.

Start with this deliberately broken program.

fn main() {
    let wide: Int = 42;
    let count: I32 = wide;
    println(count);
}

xen check class_numeric.xen

Diagnostic excerpt:

expected I32, found Int (I64)

Completion: It prints 42 with an explicit conversion; explain that out-of-range conversions fail.

Hint: Use i32(...); narrowing is not implicit.

Verify and record

Use xen check file.xen followed by xen run file.xen for ordinary programs; use xen test file.xen for test-only files. Record the original error, its cause, and the corrected result, then rerun every input in the completion criteria.