builtin: add input_character/0 and print_character/1 (#19502)

vlib/builtin/character_inout.c.v

@@ -0,0 +1,43 @@
+module builtin
+
+// input_character gives back a single character, read from the standard input.
+// It returns -1 on error (when the input is finished (EOF), on a broken pipe etc).
+pub fn input_character() int {
+	mut ch := 0
+	$if freestanding {
+		// TODO
+		return -1
+	} $else $if vinix {
+		// TODO
+		return -1
+	} $else {
+		ch = C.getchar()
+		if ch == C.EOF {
+			return -1
+		}
+	}
+	return ch
+}
+
+// print_character writes the single character `ch` to the standard output.
+// It returns -1 on error (when the output is closed, on a broken pipe, etc).
+// Note: this function does not allocate memory, unlike `print(ch.ascii_str())`
+// which does, and is thus cheaper to call, which is important, if you have
+// to output many characters one by one. If you instead want to print entire
+// strings at once, use `print(your_string)`.
+pub fn print_character(ch u8) int {
+	$if android && !termux {
+		C.android_print(C.stdout, c'%.*s', 1, voidptr(&ch))
+	} $else $if freestanding {
+		bare_print(voidptr(&ch), u64(1))
+	} $else $if vinix {
+		// TODO
+		return 0
+	} $else {
+		x := C.putchar(ch)
+		if x == C.EOF {
+			return -1
+		}
+	}
+	return ch
+}

vlib/builtin/character_inout_test.v

@@ -0,0 +1,18 @@
+fn test_print_character() {
+	assert print_character(u8(`a`)) > 0
+	assert print_character(u8(`A`)) > 0
+	println('')
+	assert print_character(rune(`a`)) > 0
+	assert print_character(rune(`A`)) > 0
+	println('')
+	assert print_character(u8(char(`a`))) > 0
+	assert print_character(u8(char(`A`))) > 0
+	println('')
+	assert print_character(u8(int(`a`))) > 0
+	assert print_character(u8(int(`A`))) > 0
+	println('')
+}
+
+fn test_input_character() {
+	// TODO: add an `expect` based test on Linux
+}