>>946
これでよろしいか。

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

int main(void)
{
int ch, count['z'-'a'+1], i;
memset(count, 0, sizeof(int)*('z'-'a'+1));
while(EOF != (ch=getc(stdin))) if(isalpha(ch)) count[(isupper(ch)?tolower(ch):ch)-'a']++;
for(i=0; i<'z'-'a'+1; i++) printf("%c : %d\n", 'a'+i, count[i]);
return 0;
}