一个简单的C问题

给一个最简单的C程序~

#include
int main(void)
{
printf("hello!");
return 0;
}

你是刚开始学C语言吧,呵呵,这个就是最简单的了,而且移植性很好,任何一款C编译器都可以通过编译,并且在linux系统上也可以编译和运行.
简单解释一下:
printf("hello!");会在屏幕上输出hello!这句话,你可以把双引号中的内容换成你想要显示的内容.

问题不大，你只需要在gets(word);前面添加一句scanf（“%c”,&c）,用于接收空格字符就行（记得再定义一个c）；
还有一个问题，你的程序就统计小写字母对，其他的都是错的，尽量自己解决，不行的话再追问我！
不明白继续追问

标准输入输出库函数。源码如下：
/*
* stdio.h
* This file has no copyright assigned and is placed in the Public Domain.
* This file is a part of the mingw-runtime package.
* No warranty is given; refer to the file DISCLAIMER within the package.
*
* Definitions of types and prototypes of functions for standard input and
* output.
*
* NOTE: The file manipulation functions provided by Microsoft seem to
* work with either slash (/) or backslash (\) as the directory separator.
*
*/

#ifndef _STDIO_H_
#define _STDIO_H_

/* All the headers include this file. */
#include <_mingw.h>

#ifndef RC_INVOKED
#define __need_size_t
#define __need_NULL
#define __need_wchar_t
#define __need_wint_t
#include <stddef.h>
#define __need___va_list
#include <stdarg.h>
#endif /* Not RC_INVOKED */

/* Flags for the iobuf structure */
#define _IOREAD 1 /* currently reading */
#define _IOWRT 2 /* currently writing */
#define _IORW 0x0080 /* opened as "r+w" */

/*
* The three standard file pointers provided by the run time library.
* NOTE: These will go to the bit-bucket silently in GUI applications!
*/
#define STDIN_FILENO 0
#define STDOUT_FILENO 1
#define STDERR_FILENO 2

/* Returned by various functions on end of file condition or error. */
#define EOF (-1)

/*
* The maximum length of a file name. You should use GetVolumeInformation
* instead of this constant. But hey, this works.
* Also defined in io.h.
*/
#ifndef FILENAME_MAX
#define FILENAME_MAX (260)
#endif

/*
* The maximum number of files that may be open at once. I have set this to
* a conservative number. The actual value may be higher.
*/
#define FOPEN_MAX (20)

/* After creating this many names, tmpnam and tmpfile return NULL */
#define TMP_MAX 32767
/*
* Tmpnam, tmpfile and, sometimes, _tempnam try to create
* temp files in the root directory of the current drive
* (not in pwd, as suggested by some older MS doc's).
* Redefining these macros does not effect the CRT functions.
*/
#define _P_tmpdir "\\"
#ifndef __STRICT_ANSI__
#define P_tmpdir _P_tmpdir
#endif
#define _wP_tmpdir L"\\"

/*
* The maximum size of name (including NUL) that will be put in the user
* supplied buffer caName for tmpnam.
* Inferred from the size of the static buffer returned by tmpnam
* when passed a NULL argument. May actually be smaller.
*/
#define L_tmpnam (16)

#define _IOFBF 0x0000 /* full buffered */
#define _IOLBF 0x0040 /* line buffered */
#define _IONBF 0x0004 /* not buffered */

#define _IOMYBUF 0x0008 /* stdio malloc()'d buffer */
#define _IOEOF 0x0010 /* EOF reached on read */
#define _IOERR 0x0020 /* I/O error from system */
#define _IOSTRG 0x0040 /* Strange or no file descriptor */
#ifdef _POSIX_SOURCE
# define _IOAPPEND 0x0200
#endif
/*
* The buffer size as used by setbuf such that it is equivalent to
* (void) setvbuf(fileSetBuffer, caBuffer, _IOFBF, BUFSIZ).
*/
#define BUFSIZ 512

/* Constants for nOrigin indicating the position relative to which fseek
* sets the file position. Enclosed in ifdefs because io.h could also
* define them. (Though not anymore since io.h includes this file now.) */
#ifndef SEEK_SET
#define SEEK_SET (0)
#endif

#ifndef SEEK_CUR
#define SEEK_CUR (1)
#endif

#ifndef SEEK_END
#define SEEK_END (2)
#endif

#ifndef RC_INVOKED

#ifndef __VALIST
#ifdef __GNUC__
#define __VALIST __gnuc_va_list
#else
#define __VALIST char*
#endif
#endif /* defined __VALIST */

/*
* The structure underlying the FILE type.
*
* Some believe that nobody in their right mind should make use of the
* internals of this structure. Provided by Pedro A. Aranda Gutiirrez
* <paag@tid.es>.
*/
#ifndef _FILE_DEFINED
#define _FILE_DEFINED
typedef struct _iobuf
{
char* _ptr;
int _cnt;
char* _base;
int _flag;
int _file;
int _charbuf;
int _bufsiz;
char* _tmpfname;
} FILE;
#endif /* Not _FILE_DEFINED */

/*
* The standard file handles
*/
#ifndef __DECLSPEC_SUPPORTED

extern FILE (*_imp___iob)[]; /* A pointer to an array of FILE */

#define _iob (*_imp___iob) /* An array of FILE */

#else /* __DECLSPEC_SUPPORTED */

__MINGW_IMPORT FILE _iob[]; /* An array of FILE imported from DLL. */

#endif /* __DECLSPEC_SUPPORTED */

#define stdin (&_iob[STDIN_FILENO])
#define stdout (&_iob[STDOUT_FILENO])
#define stderr (&_iob[STDERR_FILENO])

#ifdef __cplusplus
extern "C" {
#endif

/*
* File Operations
*/
_CRTIMP FILE* __cdecl fopen (const char*, const char*);
_CRTIMP FILE* __cdecl freopen (const char*, const char*, FILE*);
_CRTIMP int __cdecl fflush (FILE*);
_CRTIMP int __cdecl fclose (FILE*);
/* MS puts remove & rename (but not wide versions) in io.h also */
_CRTIMP int __cdecl remove (const char*);
_CRTIMP int __cdecl rename (const char*, const char*);
_CRTIMP FILE* __cdecl tmpfile (void);
_CRTIMP char* __cdecl tmpnam (char*);

#ifndef __STRICT_ANSI__
_CRTIMP char* __cdecl _tempnam (const char*, const char*);
_CRTIMP int __cdecl _rmtmp(void);

#ifndef NO_OLDNAMES
_CRTIMP char* __cdecl tempnam (const char*, const char*);
_CRTIMP int __cdecl rmtmp(void);
#endif
#endif /* __STRICT_ANSI__ */

_CRTIMP int __cdecl setvbuf (FILE*, char*, int, size_t);

_CRTIMP void __cdecl setbuf (FILE*, char*);

/*
* Formatted Output
*/

_CRTIMP int __cdecl fprintf (FILE*, const char*, ...);
_CRTIMP int __cdecl printf (const char*, ...);
_CRTIMP int __cdecl sprintf (char*, const char*, ...);
_CRTIMP int __cdecl _snprintf (char*, size_t, const char*, ...);
_CRTIMP int __cdecl vfprintf (FILE*, const char*, __VALIST);
_CRTIMP int __cdecl vprintf (const char*, __VALIST);
_CRTIMP int __cdecl vsprintf (char*, const char*, __VALIST);
_CRTIMP int __cdecl _vsnprintf (char*, size_t, const char*, __VALIST);

#ifndef __NO_ISOCEXT /* externs in libmingwex.a */
int __cdecl snprintf(char* s, size_t n, const char* format, ...);
__CRT_INLINE int __cdecl
vsnprintf (char* s, size_t n, const char* format, __VALIST arg)
{ return _vsnprintf ( s, n, format, arg); }
int __cdecl vscanf (const char * __restrict__, __VALIST);
int __cdecl vfscanf (FILE * __restrict__, const char * __restrict__,
__VALIST);
int __cdecl vsscanf (const char * __restrict__,
const char * __restrict__, __VALIST);
#endif

/*
* Formatted Input
*/

_CRTIMP int __cdecl fscanf (FILE*, const char*, ...);
_CRTIMP int __cdecl scanf (const char*, ...);
_CRTIMP int __cdecl sscanf (const char*, const char*, ...);
/*
* Character Input and Output Functions
*/

_CRTIMP int __cdecl fgetc (FILE*);
_CRTIMP char* __cdecl fgets (char*, int, FILE*);
_CRTIMP int __cdecl fputc (int, FILE*);
_CRTIMP int __cdecl fputs (const char*, FILE*);
_CRTIMP char* __cdecl gets (char*);
_CRTIMP int __cdecl puts (const char*);
_CRTIMP int __cdecl ungetc (int, FILE*);

/* Traditionally, getc and putc are defined as macros. but the
standard doesn't say that they must be macros.
We use inline functions here to allow the fast versions
to be used in C++ with namespace qualification, eg., ::getc.

_filbuf and _flsbuf are not thread-safe. */
_CRTIMP int __cdecl _filbuf (FILE*);
_CRTIMP int __cdecl _flsbuf (int, FILE*);

#if !defined _MT

__CRT_INLINE int __cdecl getc (FILE* __F)
{
return (--__F->_cnt >= 0)
? (int) (unsigned char) *__F->_ptr++
: _filbuf (__F);
}

__CRT_INLINE int __cdecl putc (int __c, FILE* __F)
{
return (--__F->_cnt >= 0)
? (int) (unsigned char) (*__F->_ptr++ = (char)__c)
: _flsbuf (__c, __F);
}

__CRT_INLINE int __cdecl getchar (void)
{
return (--stdin->_cnt >= 0)
? (int) (unsigned char) *stdin->_ptr++
: _filbuf (stdin);
}

__CRT_INLINE int __cdecl putchar(int __c)
{
return (--stdout->_cnt >= 0)
? (int) (unsigned char) (*stdout->_ptr++ = (char)__c)
: _flsbuf (__c, stdout);}

#else /* Use library functions. */

_CRTIMP int __cdecl getc (FILE*);
_CRTIMP int __cdecl putc (int, FILE*);
_CRTIMP int __cdecl getchar (void);
_CRTIMP int __cdecl putchar (int);

#endif

/*
* Direct Input and Output Functions
*/

_CRTIMP size_t __cdecl fread (void*, size_t, size_t, FILE*);
_CRTIMP size_t __cdecl fwrite (const void*, size_t, size_t, FILE*);

/*
* File Positioning Functions
*/

_CRTIMP int __cdecl fseek (FILE*, long, int);
_CRTIMP long __cdecl ftell (FILE*);
_CRTIMP void __cdecl rewind (FILE*);

#ifdef __USE_MINGW_FSEEK /* These are in libmingwex.a */
/*
* Workaround for limitations on win9x where a file contents are
* not zero'd out if you seek past the end and then write.
*/

int __cdecl __mingw_fseek (FILE *, long, int);
int __cdecl __mingw_fwrite (const void*, size_t, size_t, FILE*);
#define fseek(fp, offset, whence) __mingw_fseek(fp, offset, whence)
#define fwrite(buffer, size, count, fp) __mingw_fwrite(buffer, size, count, fp)
#endif /* __USE_MINGW_FSEEK */

/*
* An opaque data type used for storing file positions... The contents of
* this type are unknown, but we (the compiler) need to know the size
* because the programmer using fgetpos and fsetpos will be setting aside
* storage for fpos_t structres. Actually I tested using a byte array and
* it is fairly evident that the fpos_t type is a long (in CRTDLL.DLL).
* Perhaps an unsigned long? TODO? It's definitely a 64-bit number in
* MSVCRT however, and for now `long long' will do.
*/
#ifdef __MSVCRT__
typedef long long fpos_t;
#else
typedef long fpos_t;
#endif

_CRTIMP int __cdecl fgetpos (FILE*, fpos_t*);
_CRTIMP int __cdecl fsetpos (FILE*, const fpos_t*);

/*
* Error Functions
*/

_CRTIMP int __cdecl feof (FILE*);
_CRTIMP int __cdecl ferror (FILE*);

#ifdef __cplusplus
inline int __cdecl feof (FILE* __F)
{ return __F->_flag & _IOEOF; }
inline int __cdecl ferror (FILE* __F)
{ return __F->_flag & _IOERR; }
#else
#define feof(__F) ((__F)->_flag & _IOEOF)
#define ferror(__F) ((__F)->_flag & _IOERR)
#endif

_CRTIMP void __cdecl clearerr (FILE*);
_CRTIMP void __cdecl perror (const char*);

#ifndef __STRICT_ANSI__
/*
* Pipes
*/
_CRTIMP FILE* __cdecl _popen (const char*, const char*);
_CRTIMP int __cdecl _pclose (FILE*);

#ifndef NO_OLDNAMES
_CRTIMP FILE* __cdecl popen (const char*, const char*);
_CRTIMP int __cdecl pclose (FILE*);
#endif

/*
* Other Non ANSI functions
*/
_CRTIMP int __cdecl _flushall (void);
_CRTIMP int __cdecl _fgetchar (void);
_CRTIMP int __cdecl _fputchar (int);
_CRTIMP FILE* __cdecl _fdopen (int, const char*);
_CRTIMP int __cdecl _fileno (FILE*);
_CRTIMP int __cdecl _fcloseall(void);
_CRTIMP FILE* __cdecl _fsopen(const char*, const char*, int);
#ifdef __MSVCRT__
_CRTIMP int __cdecl _getmaxstdio(void);
_CRTIMP int __cdecl _setmaxstdio(int);
#endif

#ifndef _NO_OLDNAMES
_CRTIMP int __cdecl fgetchar (void);
_CRTIMP int __cdecl fputchar (int);
_CRTIMP FILE* __cdecl fdopen (int, const char*);
_CRTIMP int __cdecl fileno (FILE*);
#endif /* Not _NO_OLDNAMES */

#define _fileno(__F) ((__F)->_file)
#ifndef _NO_OLDNAMES
#define fileno(__F) ((__F)->_file)
#endif

#if defined (__MSVCRT__) && !defined (__NO_MINGW_LFS)
#include <sys/types.h>
__CRT_INLINE FILE* __cdecl fopen64 (const char* filename, const char* mode)
{
return fopen (filename, mode);
}

int __cdecl fseeko64 (FILE*, off64_t, int);

#ifdef __USE_MINGW_FSEEK
int __cdecl __mingw_fseeko64 (FILE *, off64_t, int);
#define fseeko64(fp, offset, whence) __mingw_fseeko64(fp, offset, whence)
#endif

__CRT_INLINE off64_t __cdecl ftello64 (FILE * stream)
{
fpos_t pos;
if (fgetpos(stream, &pos))
return -1LL;
else
return ((off64_t) pos);
}
#endif /* __NO_MINGW_LFS */

#endif /* Not __STRICT_ANSI__ */

/* Wide versions */

#ifndef _WSTDIO_DEFINED
/* also in wchar.h - keep in sync */
_CRTIMP int __cdecl fwprintf (FILE*, const wchar_t*, ...);
_CRTIMP int __cdecl wprintf (const wchar_t*, ...);
_CRTIMP int __cdecl swprintf (wchar_t*, const wchar_t*, ...);
_CRTIMP int __cdecl _snwprintf (wchar_t*, size_t, const wchar_t*, ...);
_CRTIMP int __cdecl vfwprintf (FILE*, const wchar_t*, __VALIST);
_CRTIMP int __cdecl vwprintf (const wchar_t*, __VALIST);
_CRTIMP int __cdecl vswprintf (wchar_t*, const wchar_t*, __VALIST);
_CRTIMP int __cdecl _vsnwprintf (wchar_t*, size_t, const wchar_t*, __VALIST);
_CRTIMP int __cdecl fwscanf (FILE*, const wchar_t*, ...);
_CRTIMP int __cdecl wscanf (const wchar_t*, ...);
_CRTIMP int __cdecl swscanf (const wchar_t*, const wchar_t*, ...);
_CRTIMP wint_t __cdecl fgetwc (FILE*);
_CRTIMP wint_t __cdecl fputwc (wchar_t, FILE*);
_CRTIMP wint_t __cdecl ungetwc (wchar_t, FILE*);

#ifdef __MSVCRT__
_CRTIMP wchar_t* __cdecl fgetws (wchar_t*, int, FILE*);
_CRTIMP int __cdecl fputws (const wchar_t*, FILE*);
_CRTIMP wint_t __cdecl getwc (FILE*);
_CRTIMP wint_t __cdecl getwchar (void);
_CRTIMP wchar_t* __cdecl _getws (wchar_t*);
_CRTIMP wint_t __cdecl putwc (wint_t, FILE*);
_CRTIMP int __cdecl _putws (const wchar_t*);
_CRTIMP wint_t __cdecl putwchar (wint_t);
_CRTIMP FILE* __cdecl _wfdopen(int, wchar_t *);
_CRTIMP FILE* __cdecl _wfopen (const wchar_t*, const wchar_t*);
_CRTIMP FILE* __cdecl _wfreopen (const wchar_t*, const wchar_t*, FILE*);
_CRTIMP FILE* __cdecl _wfsopen (const wchar_t*, const wchar_t*, int);
_CRTIMP wchar_t* __cdecl _wtmpnam (wchar_t*);
_CRTIMP wchar_t* __cdecl _wtempnam (const wchar_t*, const wchar_t*);
_CRTIMP int __cdecl _wrename (const wchar_t*, const wchar_t*);
_CRTIMP int __cdecl _wremove (const wchar_t*);
_CRTIMP void __cdecl _wperror (const wchar_t*);
_CRTIMP FILE* __cdecl _wpopen (const wchar_t*, const wchar_t*);
#endif /* __MSVCRT__ */

#ifndef __NO_ISOCEXT /* externs in libmingwex.a */
int __cdecl snwprintf (wchar_t* s, size_t n, const wchar_t* format, ...);
__CRT_INLINE int __cdecl
vsnwprintf (wchar_t* s, size_t n, const wchar_t* format, __VALIST arg)
{ return _vsnwprintf ( s, n, format, arg);}
int __cdecl vwscanf (const wchar_t * __restrict__, __VALIST);
int __cdecl vfwscanf (FILE * __restrict__,
const wchar_t * __restrict__, __VALIST);
int __cdecl vswscanf (const wchar_t * __restrict__,
const wchar_t * __restrict__, __VALIST);
#endif

#define _WSTDIO_DEFINED
#endif /* _WSTDIO_DEFINED */

#ifndef __STRICT_ANSI__
#ifdef __MSVCRT__
#ifndef NO_OLDNAMES
_CRTIMP FILE* __cdecl wpopen (const wchar_t*, const wchar_t*);
#endif /* not NO_OLDNAMES */
#endif /* MSVCRT runtime */

/*
* Other Non ANSI wide functions
*/
_CRTIMP wint_t __cdecl _fgetwchar (void);
_CRTIMP wint_t __cdecl _fputwchar (wint_t);
_CRTIMP int __cdecl _getw (FILE*);
_CRTIMP int __cdecl _putw (int, FILE*);

#ifndef _NO_OLDNAMES
_CRTIMP wint_t __cdecl fgetwchar (void);
_CRTIMP wint_t __cdecl fputwchar (wint_t);
_CRTIMP int __cdecl getw (FILE*);
_CRTIMP int __cdecl putw (int, FILE*);
#endif /* Not _NO_OLDNAMES */

#endif /* __STRICT_ANSI */

#ifdef __cplusplus
}
#endif

#endif /* Not RC_INVOKED */

#endif /* _STDIO_H_ */

标准输入输出库

standard input/output

标准输入设备通常指键盘。

标准输出设备为显示器。

用来控制从键盘获取字符，和把字符显示到显示器。

---

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