来自"NOCOW"

太简单了，逐个模拟判断
 
Pascal版
var ch:char;
    bk:boolean;
begin
    bk:=true;
    while not eof(input) do begin
        read(ch);
        if (ch>='A')and(ch<='z') then begin
            if bk then begin
                write(ch);
                bk:=false;
            end else write(chr(ord(ch)+32));
        end else if (ch='.')or(ch='?')or(ch='!') then begin
            bk:=true;
            write(ch);
        end else write(ch);
    end;
end.
//by yzxshuaige123

太简单了，逐个模拟判断
c++版：
#include<stdio.h>
#include<string.h>
 
int main(){
  char c;
  bool bk=1;
  while(scanf("%c",&c)!=EOF){
    if(c>='A'&&c<='z'){
      if(bk){ printf("%c",c);bk=0;}
      else printf("%c",c+32);
    } else if(c=='.'||c=='?'||c=='!') {bk=1;printf("%c",c);}
    else printf("%c",c);
  }
  return 0;
}
 
 
//by yzxshuaige123(楼下那几匹菜鸟还说我不行^^,哈哈，c++与PASCAL并存）

#include<stdio.h>
#include<ctype.h>
int main()
{
    int n;
    char ch;
    bool b=false;
    while (scanf("%c",&ch)!=EOF)
    {
       if(!b)
       {
         if(isalpha(ch)) b=true;
         if(ch<='z'&&ch>='a')
           printf("%c",ch-32);
         else printf("%c",ch);
         if(ch=='.'||ch=='?'||ch=='!') b=false;
       }
       else{
         if(ch<='Z'&&ch>='A') printf("%c",ch+32);
         else printf("%c",ch);
         if(ch=='.'||ch=='?'||ch=='!') b=false;
       }
    }
    return 0;
}
//by rzhpp

#include<stdio.h>
#include<ctype.h>
#include<string.h>
 
char s[10001]={0},tmp[10001]={0};
 
void downcase()
{
    int i;
    for(i=0;i<strlen(s);i++)
        if((isalpha(s[i]))&&(s[i]<97))
            s[i]+=32;
}
 
bool find(int x)
{
    while((x-1>=0))
    {
        if(isalpha(s[x-1]))return false;
        if((s[x-1]=='.')||(s[x-1]=='!')||(s[x-1]=='?'))return true;
        x-=1;
    }
    return true;
}
 
int main()
{
    int i,len,len2;
    while(gets(tmp))
    {
        len=strlen(s);
        for(i=0;i<strlen(tmp);i++)
            s[len+i]=tmp[i];
        s[len+i]='\n';s[len+i+1]='\0';
    }
        downcase();
        for(i=0;i<strlen(s);i++)
            if((isalpha(s[i]))&&(find(i)))
                s[i]-=32;
        puts(s);
    return 0;
}
//by wzm