关于C语言中if else的用法，高手来帮下忙

Posted 2023-05-06

if ~
else if
else if
else
和
if ~
else
if

else
if

else


1：以上这两种if else结构用法相同吗？2：第一种属于嵌套类型吗？还是像书上说的是基本多分枝选择结构。谢谢了！

if-else-if形式
当有多个分支选择时，可采用if-else-if语句，其一般形式为：
if(表达式1)
语句1；
else if(表达式2)
语句2；
else if(表达式3)
语句3；
…
else if(表达式m)
语句m；
else
语句n；
其语义是：依次判断表达式的值，当出现某个值为真时，则执行其对应的语句。然后跳到整个if语句之外继续执行程序。 如果所有的表达式均为假，则执行语句n。然后继续执行后续程序。 if-else-if语句的执行过程如图3—3所示。

【例】
#include"stdio.h"
main()

char c;
printf("input a character: ");
c=getchar();
if(c<32)
printf("This is a control character\n");
else if(c>='0'&&c<='9')
printf("This is a digit\n");
else if(c>='A'&&c<='Z')
printf("This is a capital letter\n");
else if(c>='a'&&c<='z')
printf("This is a small letter\n");
else
printf("This is an other character\n");


本例要求判别键盘输入字符的类别。可以根据输入字符的ASCII码来判别类型。由ASCII码表可知ASCII值小于32的为控制字符。 在“0”和“9”之间的为数字，在“A”和“Z”之间为大写字母， 在“a”和“z”之间为小写字母，其余则为其它字符。 这是一个多分
支选择的问题，用if-else-if语句编程，判断输入字符ASCII码所在的范围，分别给出不同的输出。例如输入为“g”，输出显示它为小写字符。

在使用if语句中还应注意以下问题:
1) 在三种形式的if语句中，在if关键字之后均为表达式。 该表达式通常是逻辑表达式或关系表达式， 但也可以是其它表达式，如赋值表达式等，甚至也可以是一个变量。
例如：
if(a=5) 语句；
if(b) 语句；
都是允许的。只要表达式的值为非0，即为“真”。
如在:
if(a=5)…；
中表达式的值永远为非0，所以其后的语句总是要执行的，当然这种情况在程序中不一定会出现，但在语法上是合法的。
又如，有程序段：
if(a=b)
printf("%d",a);
else
printf("a=0");
本语句的语义是，把b值赋予a，如为非0则输出该值，否则输出“a=0”字符串。这种用法在程序中是经常出现的。
2) 在if语句中，条件判断表达式必须用括号括起来，在语句之后必须加分号。
3) 在if语句的三种形式中，所有的语句应为单个语句，如果要想在满足条件时执行一组(多个)语句，则必须把这一组语句用括起来组成一个复合语句。但要注意的是在之后不能再加分号。
例如：
if(a>b)
a++;
b++;
else
a=0;
b=10; 参考技术A 如果你第二种 else 里面的两个 else内容相同，就和第一种一样了
至于理论，我不就不太清楚了

你搞不清楚逻辑的时候，可以画图帮助理解
比如你画一个饼，if就是吃了的，else就是剩下的 参考技术B 不相同. 参考技术C 这个问题只要明白程序的流程就好，不必分得这么细致吧。。。 参考技术D 我C语言考过了2级，不过现在全忘了

C语言高手帮下忙！

1、计算n阶矩阵的两条对角线上的元素的乘积。

2、统计通过键盘输入文件名，统计该文件名下的文件里字符的个数！！

用C语言表达！！！

1.for(i1=0;i1<n;i1++)
for(i2=n;i2>0;i2--)
sum+=a[i1][i1]*a[i1][i2];

2.我用语法生成器生成的c：

/* A lexical scanner generated by flex */

/* Scanner skeleton version:
* $Header: /home/daffy/u0/vern/flex/RCS/flex.skl,v 2.85 95/04/24 10:48:47 vern Exp $
*/

#define FLEX_SCANNER
#define YY_FLEX_MAJOR_VERSION 2
#define YY_FLEX_MINOR_VERSION 5

#include <stdio.h>

/* cfront 1.2 defines "c_plusplus" instead of "__cplusplus" */
#ifdef c_plusplus
#ifndef __cplusplus
#define __cplusplus
#endif
#endif

#ifdef __cplusplus

#include <stdlib.h>
#include <unistd.h>

/* Use prototypes in function declarations. */
#define YY_USE_PROTOS

/* The "const" storage-class-modifier is valid. */
#define YY_USE_CONST

#else /* ! __cplusplus */

#if __STDC__

#define YY_USE_PROTOS
#define YY_USE_CONST

#endif /* __STDC__ */
#endif /* ! __cplusplus */

#ifdef __TURBOC__
#pragma warn -rch
#pragma warn -use
#include <io.h>
#include <stdlib.h>
#define YY_USE_CONST
#define YY_USE_PROTOS
#endif

#ifdef YY_USE_CONST
#define yyconst const
#else
#define yyconst
#endif

#ifdef YY_USE_PROTOS
#define YY_PROTO(proto) proto
#else
#define YY_PROTO(proto) ()
#endif

/* Returned upon end-of-file. */
#define YY_NULL 0

/* Promotes a possibly negative, possibly signed char to an unsigned
* integer for use as an array index. If the signed char is negative,
* we want to instead treat it as an 8-bit unsigned char, hence the
* double cast.
*/
#define YY_SC_TO_UI(c) ((unsigned int) (unsigned char) c)

/* Enter a start condition. This macro really ought to take a parameter,
* but we do it the disgusting crufty way forced on us by the ()-less
* definition of BEGIN.
*/
#define BEGIN yy_start = 1 + 2 *

/* Translate the current start state into a value that can be later handed
* to BEGIN to return to the state. The YYSTATE alias is for lex
* compatibility.
*/
#define YY_START ((yy_start - 1) / 2)
#define YYSTATE YY_START

/* Action number for EOF rule of a given start state. */
#define YY_STATE_EOF(state) (YY_END_OF_BUFFER + state + 1)

/* Special action meaning "start processing a new file". */
#define YY_NEW_FILE yyrestart( yyin )

#define YY_END_OF_BUFFER_CHAR 0

/* Size of default input buffer. */
#define YY_BUF_SIZE 16384

typedef struct yy_buffer_state *YY_BUFFER_STATE;

extern int yyleng;
extern FILE *yyin, *yyout;

#define EOB_ACT_CONTINUE_SCAN 0
#define EOB_ACT_END_OF_FILE 1
#define EOB_ACT_LAST_MATCH 2

/* The funky do-while in the following #define is used to turn the definition
* int a single C statement (which needs a semi-colon terminator). This
* avoids problems with code like:
*
* if ( condition_holds )
* yyless( 5 );
* else
* do_something_else();
*
* Prior to using the do-while the compiler would get upset at the
* "else" because it interpreted the "if" statement as being all
* done when it reached the \';\' after the yyless() call.
*/

/* Return all but the first \'n\' matched characters back to the input stream. */

#define yyless(n) \\
do \\
\\
/* Undo effects of setting up yytext. */ \\
*yy_cp = yy_hold_char; \\
yy_c_buf_p = yy_cp = yy_bp + n - YY_MORE_ADJ; \\
YY_DO_BEFORE_ACTION; /* set up yytext again */ \\
\\
while ( 0 )

#define unput(c) yyunput( c, yytext_ptr )

/* The following is because we cannot portably get our hands on size_t
* (without autoconf\'s help, which isn\'t available because we want
* flex-generated scanners to compile on their own).
*/
typedef unsigned int yy_size_t;

struct yy_buffer_state

FILE *yy_input_file;

char *yy_ch_buf; /* input buffer */
char *yy_buf_pos; /* current position in input buffer */

/* Size of input buffer in bytes, not including room for EOB
* characters.
*/
yy_size_t yy_buf_size;

/* Number of characters read into yy_ch_buf, not including EOB
* characters.
*/
int yy_n_chars;

/* Whether we "own" the buffer - i.e., we know we created it,
* and can realloc() it to grow it, and should free() it to
* delete it.
*/
int yy_is_our_buffer;

/* Whether this is an "interactive" input source; if so, and
* if we\'re using stdio for input, then we want to use getc()
* instead of fread(), to make sure we stop fetching input after
* each newline.
*/
int yy_is_interactive;

/* Whether we\'re considered to be at the beginning of a line.
* If so, \'^\' rules will be active on the next match, otherwise
* not.
*/
int yy_at_bol;

/* Whether to try to fill the input buffer when we reach the
* end of it.
*/
int yy_fill_buffer;

int yy_buffer_status;
#define YY_BUFFER_NEW 0
#define YY_BUFFER_NORMAL 1
/* When an EOF\'s been seen but there\'s still some text to process
* then we mark the buffer as YY_EOF_PENDING, to indicate that we
* shouldn\'t try reading from the input source any more. We might
* still have a bunch of tokens to match, though, because of
* possible backing-up.
*
* When we actually see the EOF, we change the status to "new"
* (via yyrestart()), so that the user can continue scanning by
* just pointing yyin at a new input file.
*/
#define YY_BUFFER_EOF_PENDING 2
;

static YY_BUFFER_STATE yy_current_buffer = 0;

/* We provide macros for accessing buffer states in case in the
* future we want to put the buffer states in a more general
* "scanner state".
*/
#define YY_CURRENT_BUFFER yy_current_buffer

/* yy_hold_char holds the character lost when yytext is formed. */
static char yy_hold_char;

static int yy_n_chars; /* number of characters read into yy_ch_buf */

int yyleng;

/* Points to current character in buffer. */
static char *yy_c_buf_p = (char *) 0;
static int yy_init = 1; /* whether we need to initialize */
static int yy_start = 0; /* start state number */

/* Flag which is used to allow yywrap()\'s to do buffer switches
* instead of setting up a fresh yyin. A bit of a hack ...
*/
static int yy_did_buffer_switch_on_eof;

void yyrestart YY_PROTO(( FILE *input_file ));

void yy_switch_to_buffer YY_PROTO(( YY_BUFFER_STATE new_buffer ));
void yy_load_buffer_state YY_PROTO(( void ));
YY_BUFFER_STATE yy_create_buffer YY_PROTO(( FILE *file, int size ));
void yy_delete_buffer YY_PROTO(( YY_BUFFER_STATE b ));
void yy_init_buffer YY_PROTO(( YY_BUFFER_STATE b, FILE *file ));
void yy_flush_buffer YY_PROTO(( YY_BUFFER_STATE b ));
#define YY_FLUSH_BUFFER yy_flush_buffer( yy_current_buffer )

YY_BUFFER_STATE yy_scan_buffer YY_PROTO(( char *base, yy_size_t size ));
YY_BUFFER_STATE yy_scan_string YY_PROTO(( yyconst char *str ));
YY_BUFFER_STATE yy_scan_bytes YY_PROTO(( yyconst char *bytes, int len ));

static void *yy_flex_alloc YY_PROTO(( yy_size_t ));
static void *yy_flex_realloc YY_PROTO(( void *, yy_size_t ));
static void yy_flex_free YY_PROTO(( void * ));

#define yy_new_buffer yy_create_buffer

#define yy_set_interactive(is_interactive) \\
\\
if ( ! yy_current_buffer ) \\
yy_current_buffer = yy_create_buffer( yyin, YY_BUF_SIZE ); \\
yy_current_buffer->yy_is_interactive = is_interactive; \\


#define yy_set_bol(at_bol) \\
\\
if ( ! yy_current_buffer ) \\
yy_current_buffer = yy_create_buffer( yyin, YY_BUF_SIZE ); \\
yy_current_buffer->yy_at_bol = at_bol; \\


#define YY_AT_BOL() (yy_current_buffer->yy_at_bol)

typedef unsigned char YY_CHAR;
FILE *yyin = (FILE *) 0, *yyout = (FILE *) 0;
typedef int yy_state_type;
extern char *yytext;
#define yytext_ptr yytext

static yy_state_type yy_get_previous_state YY_PROTO(( void ));
static yy_state_type yy_try_NUL_trans YY_PROTO(( yy_state_type current_state ));
static int yy_get_next_buffer YY_PROTO(( void ));
static void yy_fatal_error YY_PROTO(( yyconst char msg[] ));

/* Done after the current pattern has been matched and before the
* corresponding action - sets up yytext.
*/
#define YY_DO_BEFORE_ACTION \\
yytext_ptr = yy_bp; \\
yyleng = (int) (yy_cp - yy_bp); \\
yy_hold_char = *yy_cp; \\
*yy_cp = \'\\0\'; \\
yy_c_buf_p = yy_cp;

#define YY_NUM_RULES 4
#define YY_END_OF_BUFFER 5
static yyconst short int yy_accept[9] =
0,
0, 0, 5, 3, 2, 1, 1, 0
;

static yyconst int yy_ec[256] =
0,
1, 1, 1, 1, 1, 1, 1, 1, 1, 2,
1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 3, 3, 3,
3, 3, 3, 3, 3, 3, 3, 1, 1, 1,
1, 1, 1, 1, 3, 3, 3, 3, 3, 3,
3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
1, 1, 1, 1, 1, 1, 3, 3, 3, 3,

3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
3, 3, 3, 3, 3, 3, 3, 3, 3, 3,
3, 3, 1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1, 1, 1,

1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1
;

static yyconst int yy_meta[4] =
0,
1, 1, 2
;

static yyconst short int yy_base[10] =
0,
0, 0, 5, 6, 6, 0, 0, 6, 2
;

static yyconst short int yy_def[10] =
0,
8, 1, 8, 8, 8, 9, 9, 0, 8
;

static yyconst short int yy_nxt[10] =
0,
4, 5, 6, 7, 8, 3, 8, 8, 8
;

static yyconst short int yy_chk[10] =
0,
1, 1, 1, 9, 3, 8, 8, 8, 8
;

static yy_state_type yy_last_accepting_state;
static char *yy_last_accepting_cpos;

/* The intent behind this definition is that it\'ll catch
* any uses of REJECT which flex missed.
*/
#define REJECT reject_used_but_not_detected
#define yymore() yymore_used_but_not_detected
#define YY_MORE_ADJ 0
char *yytext;
#line 1 "lex.l"
#define INITIAL 0
#line 2 "lex.l"
/*a lex program for counting the number of character, word and line in the input file*/
#include <stdio.h>
#include <string.h>

/*the line count*/
int iLineNo = 0;
/*the character counter*/
int iCharNo = 0;
/*the word counter*/
int iWordNo = 0;
#line 372 "lex.yy.c"

/* Macros after this point can all be overridden by user definitions in
* section 1.
*/

#ifndef YY_SKIP_YYWRAP
#ifdef __cplusplus
extern "C" int yywrap YY_PROTO(( void ));
#else
extern int yywrap YY_PROTO(( void ));
#endif
#endif

#ifndef YY_NO_UNPUT
static void yyunput YY_PROTO(( int c, char *buf_ptr ));
#endif

#ifndef yytext_ptr
static void yy_flex_strncpy YY_PROTO(( char *, yyconst char *, int ));
#endif

#ifndef YY_NO_INPUT
#ifdef __cplusplus
static int yyinput YY_PROTO(( void ));
#else
static int input YY_PROTO(( void ));
#endif
#endif

#if YY_STACK_USED
static int yy_start_stack_ptr = 0;
static int yy_start_stack_depth = 0;
static int *yy_start_stack = 0;
#ifndef YY_NO_PUSH_STATE
static void yy_push_state YY_PROTO(( int new_state ));
#endif
#ifndef YY_NO_POP_STATE
static void yy_pop_state YY_PROTO(( void ));
#endif
#ifndef YY_NO_TOP_STATE
static int yy_top_state YY_PROTO(( void ));
#endif

#else
#define YY_NO_PUSH_STATE 1
#define YY_NO_POP_STATE 1
#define YY_NO_TOP_STATE 1
#endif

#ifdef YY_MALLOC_DECL
YY_MALLOC_DECL
#else
#if __STDC__
#ifndef __cplusplus
#include <stdlib.h>
#endif
#else
/* Just try to get by without declaring the routines. This will fail
* miserably on non-ANSI systems for which sizeof(size_t) != sizeof(int)
* or sizeof(void*) != sizeof(int).
*/
#endif
#endif

/* Amount of stuff to slurp up with each read. */
#ifndef YY_READ_BUF_SIZE
#define YY_READ_BUF_SIZE 8192
#endif

/* Copy whatever the last rule matched to the standard output. */

#ifndef ECHO
/* This used to be an fputs(), but since the string might contain NUL\'s,
* we now use fwrite().
*/
#define ECHO (void) fwrite( yytext, yyleng, 1, yyout )
#endif

/* Gets input and stuffs it into "buf". number of characters read, or YY_NULL,
* is returned in "result".
*/
#ifndef YY_INPUT
#define YY_INPUT(buf,result,max_size) \\
if ( yy_current_buffer->yy_is_interactive ) \\
\\
int c = \'*\', n; \\
for ( n = 0; n < max_size && \\
(c = getc( yyin )) != EOF && c != \'\\n\'; ++n ) \\
buf[n] = (char) c; \\
if ( c == \'\\n\' ) \\
buf[n++] = (char) c; \\
if ( c == EOF && ferror( yyin ) ) \\
YY_FATAL_ERROR( "input in flex scanner failed" ); \\
result = n; \\
\\
else if ( ((result = fread( buf, 1, max_size, yyin )) == 0) \\
&& ferror( yyin ) ) \\
YY_FATAL_ERROR( "input in flex scanner failed" );
#endif

/* No semi-colon after return; correct usage is to write "yyterminate();" -
* we don\'t want an extra \';\' after the "return" because that will cause
* some compilers to complain about unreachable statements.
*/
#ifndef yyterminate
#define yyterminate() return YY_NULL
#endif

/* Number of entries by which start-condition stack grows. */
#ifndef YY_START_STACK_INCR
#define YY_START_STACK_INCR 25
#endif

/* Report a fatal error. */
#ifndef YY_FATAL_ERROR
#define YY_FATAL_ERROR(msg) yy_fatal_error( msg )
#endif

/* Default declaration of generated scanner - a define so the user can
* easily add parameters.
*/
#ifndef YY_DECL
#define YY_DECL int yylex YY_PROTO(( void ))
#endif

/* Code executed at the beginning of each rule, after yytext and yyleng
* have been set up.
*/
#ifndef YY_USER_ACTION
#define YY_USER_ACTION
#endif

/* Code executed at the end of each rule. */
#ifndef YY_BREAK
#define YY_BREAK break;
#endif

#define YY_RULE_SETUP \\
YY_USER_ACTION

YY_DECL

register yy_state_type yy_current_state;
register char *yy_cp, *yy_bp;
register int yy_act;

#line 15 "lex.l"

#line 521 "lex.yy.c"

if ( yy_init )

yy_init = 0;

#ifdef YY_USER_INIT
YY_USER_INIT;
#endif

if ( ! yy_start )
yy_start = 1; /* first start state */

if ( ! yyin )
yyin = stdin;

if ( ! yyout )
yyout = stdout;

if ( ! yy_current_buffer )
yy_current_buffer =
yy_create_buffer( yyin, YY_BUF_SIZE );

yy_load_buffer_state();


while ( 1 ) /* loops until end-of-file is reached */

yy_cp = yy_c_buf_p;

/* Support of yytext. */
*yy_cp = yy_hold_char;

/* yy_bp points to the position in yy_ch_buf of the start of
* the current run.
*/
yy_bp = yy_cp;

yy_current_state = yy_start;
yy_match:
do

register YY_CHAR yy_c = yy_ec[YY_SC_TO_UI(*yy_cp)];
if ( yy_accept[yy_current_state] )

yy_last_accepting_state = yy_current_state;
yy_last_accepting_cpos = yy_cp;

while ( yy_chk[yy_base[yy_current_state] + yy_c] != yy_current_state )

yy_current_state = (int) yy_def[yy_current_state];
if ( yy_current_state >= 9 )
yy_c = yy_meta[(unsigned int) yy_c];

yy_current_state = yy_nxt[yy_base[yy_current_state] + (unsigned int) yy_c];
++yy_cp;

while ( yy_base[yy_current_state] != 6 );

yy_find_action:
yy_act = yy_accept[yy_current_state];
if ( yy_act == 0 )
/* have to back up */
yy_cp = yy_last_accepting_cpos;
yy_current_state = yy_last_accepting_state;
yy_act = yy_accept[yy_current_state];


YY_DO_BEFORE_ACTION;

do_action: /* This label is used only to access EOF actions. */

switch ( yy_act )
/* beginning of action switch */
case 0: /* must back up */
/* undo the effects of YY_DO_BEFORE_ACTION */
*yy_cp = yy_hold_char;
yy_cp = yy_last_accepting_cpos;
yy_current_state = yy_last_accepting_state;
goto yy_find_action;

case 1:
YY_RULE_SETUP
#line 16 "lex.l"
iWordNo++; iCharNo += strlen(yytext);
YY_BREAK
case 2:
YY_RULE_SETUP
#line 17 "lex.l"
iLineNo++;
YY_BREAK
case 3:
YY_RULE_SETUP
#line 18 "lex.l"
iCharNo++;
YY_BREAK
case 4:
YY_RULE_SETUP
#line 19 "lex.l"
ECHO;
YY_BREAK
#line 624 "lex.yy.c"
case YY_STATE_EOF(INITIAL):
yyterminate();

case YY_END_OF_BUFFER:

/* Amount of text matched not including the EOB char. */
int yy_amount_of_matched_text = (int) (yy_cp - yytext_ptr) - 1;

/* Undo the effects of YY_DO_BEFORE_ACTION. */
*yy_cp = yy_hold_char;

if ( yy_current_buffer->yy_buffer_status == YY_BUFFER_NEW )

/* We\'re scanning a new file or input source. It\'s
* possible that this happened because the user
* just pointed yyin at a new source and called
* yylex(). If so, then we have to assure
* consistency between yy_current_buffer and our
* globals. Here is the right place to do so, because
* this is the first action (other than possibly a
* back-up) that will match for the new input source.
*/
yy_n_chars = yy_current_buffer->yy_n_chars;
yy_current_buffer->yy_input_file = yyin;
yy_current_buffer->yy_buffer_status = YY_BUFFER_NORMAL;


/* Note that here we test for yy_c_buf_p "<=" to the position
* of the first EOB in the buffer, since yy_c_buf_p will
* already have been incremented past the NUL character
* (since all states make transitions on EOB to the
* end-of-buffer state). Contrast this with the test
* in input().
*/
if ( yy_c_buf_p <= &yy_current_buffer->yy_ch_buf[yy_n_chars] )
/* This was really a NUL. */
yy_state_type yy_next_state;

yy_c_buf_p = yytext_ptr + yy_amount_of_matched_text;

yy_current_state = yy_get_previous_state();

/* Okay, we\'re now positioned to make the NUL
* transition. We couldn\'t have
* yy_get_previous_state() go ahead and do it
* for us because it doesn\'t know how to deal
* with the possibility of jamming (and we don\'t
* want to build jamming into it because then it
* will run more slowly).
*/

yy_next_state = yy_try_NUL_trans( yy_current_state );

yy_bp = yytext_ptr + YY_MORE_ADJ;

if ( yy_next_state )

/* Consume the NUL. */
yy_cp = ++yy_c_buf_p;
yy_current_state = yy_next_state;
goto yy_match;


else

yy_cp = yy_c_buf_p;
goto yy_find_action;



else switch ( yy_get_next_buffer() )

case EOB_ACT_END_OF_FILE:

yy_did_buffer_switch_on_eof = 0;

if ( yywrap() )

/* Note: because we\'ve taken care in
* yy_get_next_buffer() to have set up
* yytext, we can now set up
* yy_c_buf_p so that if some total
* hoser (like flex itself) wants to
* call the scanner after we return the
* YY_NULL, it\'ll still work - another
* YY_NULL will get returned.
*/
yy_c_buf_p = yytext_ptr + YY_MORE_ADJ;

yy_act = YY_STATE_EOF(YY_START);
goto do_action;


else

if ( ! yy_did_buffer_switch_on_eof )
YY_NEW_FILE;

break;


case EOB_ACT_CONTINUE_SCAN:
yy_c 参考技术A 第二个


FILE *fp;
fp=fopen(\"****\",rb);////////****表示你要打开的文件路径
if(NULL==fp)
printf(\"出错了!\");exit(0);
long tt;
fseek(fp,0,2);
tt=ftell(fp);
printf(\"个数为：%l\",tt);
fclose(fp);
参考技术B 1。N阶矩阵你可以使用2维数组来存放，然后把里面的对应元素乘起来就行了
伪代码：
for(int i=0;i<=n;i++)

for(int h=0;h<=n;h++)

if(h==i)result1=result1*juzhen[h][i]; //当为对角线时候，计算乘积
if((n-h)==i))result1=result1*juzhen[n-h][i]; //当为另一对角线时候，计算乘积




result跟result1就是结果

第二题用文件流就行，定义一个变量存放文件流，文件的内容就放在变量里面

以上为伪代码 参考技术C 这两个都简单的