{
"id": "160",
"prompt": "Decimal-digits utility library (a spawn_lib target - every fn is exported): digits(n) counts decimal digits sign-safely, pow10(k) by a loop, digit_at(n, k) returns the k-th digit counting from the least-significant end, and reverse(n) turns 90210 into 1209 with a divide/mod loop. The landing frame() prints digits(90210), digit_at(90210, 2), and reverse(90210) as its own self-test.",
"solution_rl": "fn digits(n: i32) -> i32 {\n let mut v: i32 = n;\n if v < 0 { v = 0 - v; }\n let mut c: i32 = 1;\n while v >= 10 {\n v = v / 10;\n c = c + 1;\n }\n c\n}\n\nfn pow10(k: i32) -> i32 {\n let mut p: i32 = 1;\n let mut i: i32 = 0;\n while i < k {\n p = p * 10;\n i = i + 1;\n }\n p\n}\n\nfn digit_at(n: i32, k: i32) -> i32 {\n let mut v: i32 = n;\n if v < 0 { v = 0 - v; }\n let d: i32 = v / pow10(k);\n d % 10\n}\n\nfn reverse(n: i32) -> i32 {\n let mut v: i32 = n;\n if v < 0 { v = 0 - v; }\n let mut r: i32 = 0;\n while v > 0 {\n r = r * 10 + v % 10;\n v = v / 10;\n }\n r\n}\n\nfn dims() -> i32 {\n (256 << 16) | 112\n}\n\nfn frame(t: i32) {\n host::display::clear(0x000000);\n host::display::draw_string(8, 8, \"LIB DIGITS\", 0xffffff, 2);\n host::display::draw_string(8, 32, \"DIGITS POW10\", 0x00ff66, 1);\n host::display::draw_string(8, 46, \"DIGIT_AT REVERSE\", 0x00ff66, 1);\n host::display::draw_number(8, 66, digits(90210), 0xffff00, 1);\n host::display::draw_number(60, 66, digit_at(90210, 2), 0xffff00, 1);\n host::display::draw_number(112, 66, reverse(90210), 0xffff00, 1);\n host::display::present();\n}\n",
"tags": [
"library",
"functions",
"loops"
]
}