2種做法，1種用單字符來讀取輸入，1種用字符串來讀取輸入。
1.
#include <stdio.h>

int main()
{
	int i, upper, lower, digit, space, other;
	char c;
	upper = lower = digit = space = other = 0;
	for(i = 0; i < 3; i++)
		while((c = getchar()) != '\n')
			if('A' <= c && c <= 'Z')
				upper++;
			else if('a' <= c && c <= 'z')
				lower++;
			else if('0' <= c && c <= '9')
				digit++;
			else if(c == ' ')
				space++;
			else
				other++;
	printf("upper:%d\nlower:%d\ndigit:%d\nspace:%d\nother:%d\n", upper, lower, digit, space, other);
	return 0;
}
 
2.
#include <stdio.h>

int main()
{
	int i, j, upper, lower, digit, space, other;
	char str[3][81];
	upper = lower = digit = space = other = 0;
	for(i = 0; i < 3; i++)
	{
		gets(str[i]);
		for(j = 0; str[i][j]; j++)
			if('A' <= str[i][j] && str[i][j] <= 'Z')
				upper++;
			else if('a' <= str[i][j] && str[i][j] <= 'z')
				lower++;
			else if('0' <= str[i][j] && str[i][j] <= '9')
				digit++;
			else if(str[i][j] == ' ')
				space++;
			else
				other++;
	}
	printf("upper:%d\nlower:%d\ndigit:%d\nspace:%d\nother:%d\n", upper, lower, digit, space, other);
	return 0;
}