Language: C++

#include <iostream>
#include <string.h>
#include <vector>
#include <set>
#include <iomanip>

using namespace std;

typedef unsigned long long ull;
typedef pair<int, int> P;

int main()
{
	string n;
	cin >> n;

	int k;
	cin >> k;

	ull sum = 0;

	int digits = n.size();

	int ans1[10] = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };
	int ans2[100] = { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81 };
	int ans3[1000] = { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 81, 81, 81, 81, 81, 81, 81, 81, 81, 81, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 99, 100, 101, 102, 103, 104, 105, 106, 107, 108, 108, 109, 110, 111, 112, 113, 114, 115, 116, 117, 117, 118, 119, 120, 121, 122, 123, 124, 125, 126, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 144, 145, 146, 147, 148, 149, 150, 151, 152, 153, 153, 154, 155, 156, 157, 158, 159, 160, 161, 162, 162, 162, 162, 162, 162, 162, 162, 162, 162, 162, 162, 163, 164, 165, 166, 167, 168, 169, 170, 171, 171, 172, 173, 174, 175, 176, 177, 178, 179, 180, 180, 181, 182, 183, 184, 185, 186, 187, 188, 189, 189, 190, 191, 192, 193, 194, 195, 196, 197, 198, 198, 199, 200, 201, 202, 203, 204, 205, 206, 207, 207, 208, 209, 210, 211, 212, 213, 214, 215, 216, 216, 217, 218, 219, 220, 221, 222, 223, 224, 225, 225, 226, 227, 228, 229, 230, 231, 232, 233, 234, 234, 235, 236, 237, 238, 239, 240, 241, 242, 243, 243, 243, 243, 243, 243, 243, 243, 243, 243, 243, 243, 244, 245, 246, 247, 248, 249, 250, 251, 252, 252, 253, 254, 255, 256, 257, 258, 259, 260, 261, 261, 262, 263, 264, 265, 266, 267, 268, 269, 270, 270, 271, 272, 273, 274, 275, 276, 277, 278, 279, 279, 280, 281, 282, 283, 284, 285, 286, 287, 288, 288, 289, 290, 291, 292, 293, 294, 295, 296, 297, 297, 298, 299, 300, 301, 302, 303, 304, 305, 306, 306, 307, 308, 309, 310, 311, 312, 313, 314, 315, 315, 316, 317, 318, 319, 320, 321, 322, 323, 324, 324, 324, 324, 324, 324, 324, 324, 324, 324, 324, 324, 325, 326, 327, 328, 329, 330, 331, 332, 333, 333, 334, 335, 336, 337, 338, 339, 340, 341, 342, 342, 343, 344, 345, 346, 347, 348, 349, 350, 351, 351, 352, 353, 354, 355, 356, 357, 358, 359, 360, 360, 361, 362, 363, 364, 365, 366, 367, 368, 369, 369, 370, 371, 372, 373, 374, 375, 376, 377, 378, 378, 379, 380, 381, 382, 383, 384, 385, 386, 387, 387, 388, 389, 390, 391, 392, 393, 394, 395, 396, 396, 397, 398, 399, 400, 401, 402, 403, 404, 405, 405, 405, 405, 405, 405, 405, 405, 405, 405, 405, 405, 406, 407, 408, 409, 410, 411, 412, 413, 414, 414, 415, 416, 417, 418, 419, 420, 421, 422, 423, 423, 424, 425, 426, 427, 428, 429, 430, 431, 432, 432, 433, 434, 435, 436, 437, 438, 439, 440, 441, 441, 442, 443, 444, 445, 446, 447, 448, 449, 450, 450, 451, 452, 453, 454, 455, 456, 457, 458, 459, 459, 460, 461, 462, 463, 464, 465, 466, 467, 468, 468, 469, 470, 471, 472, 473, 474, 475, 476, 477, 477, 478, 479, 480, 481, 482, 483, 484, 485, 486, 486, 486, 486, 486, 486, 486, 486, 486, 486, 486, 486, 487, 488, 489, 490, 491, 492, 493, 494, 495, 495, 496, 497, 498, 499, 500, 501, 502, 503, 504, 504, 505, 506, 507, 508, 509, 510, 511, 512, 513, 513, 514, 515, 516, 517, 518, 519, 520, 521, 522, 522, 523, 524, 525, 526, 527, 528, 529, 530, 531, 531, 532, 533, 534, 535, 536, 537, 538, 539, 540, 540, 541, 542, 543, 544, 545, 546, 547, 548, 549, 549, 550, 551, 552, 553, 554, 555, 556, 557, 558, 558, 559, 560, 561, 562, 563, 564, 565, 566, 567, 567, 567, 567, 567, 567, 567, 567, 567, 567, 567, 567, 568, 569, 570, 571, 572, 573, 574, 575, 576, 576, 577, 578, 579, 580, 581, 582, 583, 584, 585, 585, 586, 587, 588, 589, 590, 591, 592, 593, 594, 594, 595, 596, 597, 598, 599, 600, 601, 602, 603, 603, 604, 605, 606, 607, 608, 609, 610, 611, 612, 612, 613, 614, 615, 616, 617, 618, 619, 620, 621, 621, 622, 623, 624, 625, 626, 627, 628, 629, 630, 630, 631, 632, 633, 634, 635, 636, 637, 638, 639, 639, 640, 641, 642, 643, 644, 645, 646, 647, 648, 648, 648, 648, 648, 648, 648, 648, 648, 648, 648, 648, 649, 650, 651, 652, 653, 654, 655, 656, 657, 657, 658, 659, 660, 661, 662, 663, 664, 665, 666, 666, 667, 668, 669, 670, 671, 672, 673, 674, 675, 675, 676, 677, 678, 679, 680, 681, 682, 683, 684, 684, 685, 686, 687, 688, 689, 690, 691, 692, 693, 693, 694, 695, 696, 697, 698, 699, 700, 701, 702, 702, 703, 704, 705, 706, 707, 708, 709, 710, 711, 711, 712, 713, 714, 715, 716, 717, 718, 719, 720, 720, 721, 722, 723, 724, 725, 726, 727, 728, 729 };
	
	/*if (k == 1)
	{
		for (int i = 0; i < digits; i++)
		{
			int num = n[i] - '0';

			if (i == 0)
			{
				sum += ans1[num];
			}
			else
			{
				sum += ans1[9];
			}
		}
	}*/

	else if (k == 2)
	{
		for (int i = 0; i < digits - 1; i++)
		{
			int iNum = n[i] - '0';
			iNum *= 10;
			for (int j = i + 1; j < digits; j++)
			{
				int jNum = n[j] - '0';
				
				if (i == 0 && j == 1)
				{
					sum += ans2[iNum + jNum];
				}
				else if (i == 0)
				{
					sum += ans2[iNum + 9];
				}
				else
				{
					sum += ans2[99];
				}
			}
		}
	}

	//else if (k == 3)
	//{
	//	for (int i = 0; i < digits - 2; i++)
	//	{
	//		int iNum = n[i] - '0';
	//		iNum *= 100;

	//		for (int j = i + 1; j < digits - 1; j++)
	//		{
	//			int jNum = n[j] - '0';
	//			jNum *= 10;

	//			for (int k = j + 1; k < digits; k++)
	//			{
	//				int kNum = n[k] - '0';

	//				if (i == 0 && j == 1 && k == 2)
	//				{
	//					sum += ans3[iNum + jNum + kNum];
	//				}
	//				else if (i == 0 && j == 1)
	//				{
	//					sum += ans3[iNum + jNum + 9];
	//				}
	//				else if (i == 0)
	//				{
	//					sum += ans3[iNum + 99];
	//				}
	//				else
	//				{
	//					sum += ans3[999];
	//				}
	//			}
	//		}
	//	}
	//}

	cout << sum << endl;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:45:9: error: 'else' without a previous 'if'
   45 |         else if (k == 2)
      |         ^~~~