interpret-3-plus-4

Read three characters, compute the sum, print it.

'3' - '0' is 3 because ASCII digits are contiguous. But Zig never converts between types implicitly, and input[0] is a u8 -- subtracting one u8 from another would panic if it ever went below zero. We widen to i64 first: @as(i64, input[0]) - '0'.

For now, the input has no spaces. "3+4", not "3 + 4". Whitespace handling comes much later.

Fill in the three // YOU lines.

pub fn main() void {
    const input: [:0]const u8 = "3+4";

    // YOU: const a: i64 = ...
    // YOU: const b: i64 = ...
    // YOU: const result: i64 = ...

    printString("interpreter result for ");
    printString(input);
    printString(" : ");
    printNumber(result);
    printChar('\n');
}

const a: i64 = @as(i64, input[0]) - '0';
const b: i64 = @as(i64, input[2]) - '0';
const result: i64 = a + b;

We're ignoring input[1]. Hardcoded + for now.

In Zig, strings are arrays of bytes. The :0 in [:0]const u8 says "ends with a zero byte" -- a sentinel we'll use as our end-of-input marker later. Don't sweat the exact punctuation; just remember the strings end with a zero.