2.程序源代码：

#include "stdio.h"

main()

{char c;

int letters=0,space=0,digit=0,others=0;

printf("please input some characters\n");

while((c=getchar())!='\n')

{

if(c>='a'&&c<='z'||c>='A'&&c<='Z')

letters++;

else if(c==' ')

space++;

else if(c>='0'&&c<='9')

digit++;

else

others++;

}

printf("all in all:char=%d space=%d digit=%d others=%d\n",letters, space,digit,others);

}

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【程序18】