5-2
こんな感じ？

#include <stdio.h>
#include <ctype.h>

int main(int argc, char* argv[]){
int ch;
int ca;

ca=0

for(; (ch=getchar())!=EOF;) {

if( isalpha(ch)) ca++;
if( islower(ch)) ca++;
if( isdigit(ch)) ca++;

}


printf("%d\n",ca);

return 0;
}