PAT/PATBasic/1078.c

#include <stdio.h>

void compress()
{
	char previous = getchar(), current;
	int count = 1;

	while ((current = getchar())) {
		if (current == previous) {
			count++;                /* Increament count */
		} else {
			if (count > 1)           /* Only print if count > 1 */
				printf("%d", count);
			putchar(previous);
			previous = current;
			count = 1;
		}

		if (current == '\n' || current == EOF)  /* Don't put this in while () */
			break;
	}
}

void decompress()
{
	char c;
	int count = 0;

	while ((c = getchar()) != EOF && c != '\n') {
		if (c >= '0' && c <= '9') { /* If it is number */
			count = count * 10 + c - '0';   /* Accumulate count */
		} else {                    /* If it is not number */
			if (count == 0)                  /* No number before char */
				count = 1;                      /* print once */
			for (int i = 0; i < count; i++)  /* Or print 'count' times */
				putchar(c);
			count = 0;                      /* Reset 'count' */
		}
	}
}

int main()
{
	switch(getchar()) {
	case 'C':
		while (getchar() != '\n');
		compress();
		break;
	case 'D':
		while (getchar() != '\n');
		decompress();
		break;
	default:
		break;
	}

	return 0;
}