我正在尝试为这个简单的词法分析器添加浮点功能，我用C编写了C语言（除此之外）。我有一些关于如何做到这一点的想法，但它们都是不完整的解决方案，主要是在Parse整数文字中加入if语句，但由于while语句，它仍然会停止并将句点计算为句点。我想在while语句中添加一个OR，但我不完全确定如何指定它只是一个句点。这是代码：
/* front.c */
#include <stdio.h>
#include <ctype.h>
#include <string.h>
#include <conio.h>
/*Global Declarations */
/*variables*/
int charClass;
char lexeme [100];
char nextChar;
int lexLen;
int token;
int nextToken;
FILE *in_fp, *fopen();
/*function declarations*/
void addChar();
void getChar();
void getNonBlank();
int lex();
/*Character classes */
#define LETTER 0
#define DIGIT 1
#define UNKNOWN 99
/*token codes*/
#define INT_LIT 10
#define FLOAT
#define IDENT 11
#define ASSIGN_OP 20
#define ADD_OP 21
#define SUB_OP 22
#define MULT_OP 23
#define DIV_OP 24
#define LEFT_PAREN 25
#define RIGHT_PAREN 26
#define MOD_OP 27
#define SEMICOL 28
#define COMMA 29
#define EXCLAMATION_MARK 30
#define AT_SIGN 31
#define POUND_SIGN 32
#define DOLLAR_SIGN 33
#define CARAT_SIGN 34
#define AMPERSAND 35
#define PERIOD_MARK 36
#define LESSTHAN_SIGN 37
#define GREATERTHAN_SIGN 38
#define QUESTION_MARK 39
#define LEFT_SQUAREBRACKET 40
#define RIGHT_SQUAREBRACKET 41
#define LEFT_CURLYBRACKET 42
#define RIGHT_CURLYBRACKET 43
#define BACKSLASH 44
#define VERTICALBAR 45
#define SINGLE_QUOTE 46
#define DOUBLE_QUOTE 47
#define COLON 48
#define UNDERSCORE 49
#define TILDE 50
#define GRAVE_ACCENT 51
/*********************/
/*main driver */
main()
{
/*Open the input data file and process its contents*/
if ((in_fp = fopen("front.in", "r")) == NULL)
printf("ERROR - cannot open front.in \n");
else
{
getChar();
do
{
lex();
} while (nextToken != EOF);
}
}
/***************************/
/*lookup - a function to lookup operators and parentheses
and return the token */
int lookup(char ch)
{
switch (ch)
{
case '=':
addChar();
nextToken = ASSIGN_OP
break;
case '(':
addChar();
nextToken = LEFT_PAREN;
break;
case ')':
addChar();
nextToken = RIGHT_PAREN;
break;
case '+':
addChar();
nextToken = ADD_OP;
break;
case '-':
addChar();
nextToken = SUB_OP;
break;
case '*':
addChar();
nextToken = MULT_OP;
break;
case '/':
addChar();
nextToken = DIV_OP;
break;
case '%':
addChar();
nextToken = MOD_OP;
break;
case ';':
addChar();
nextToken = SEMICOL;
break;
case ':':
addChar();
nextToken = COLON;
break;
case '"':
addChar();
nextToken = DOUBLE_QUOTE;
break;
case ',':
addChar();
nextToken = COMMA;
break;
case '.':
addChar();
nextToken = PERIOD_MARK;
break;
case '!':
addChar();
nextToken = EXCLAMATION_MARK;
break;
case '@':
addChar();
nextToken = AT_SIGN;
break;
case '#':
addChar();
nextToken = POUND_SIGN;
break;
case '$':
addChar();
nextToken = DOLLAR_SIGN;
break;
case '^':
addChar();
nextToken = CARAT_SIGN;
break;
case '&':
addChar();
nextToken = AMPERSAND;
break;
case '<':
addChar();
nextToken = LESSTHAN_SIGN;
break;
case '>':
addChar();
nextToken = GREATERTHAN_SIGN;
break;
case '?':
addChar();
nextToken = QUESTION_MARK;
break;
case '[':
addChar();
nextToken = LEFT_SQUAREBRACKET;
break;
case ']':
addChar();
nextToken = RIGHT_SQUAREBRACKET;
break;
case '{':
addChar();
nextToken = LEFT_CURLYBRACKET;
break;
case '}':
addChar();
nextToken = RIGHT_CURLYBRACKET;
break;
case '\'':
addChar();
nextToken = SINGLE_QUOTE;
break;*
case '|':
addChar();
nextToken = VERTICALBAR;
break;
case '_':
addChar();
nextToken = UNDERSCORE;
break;
case '~':
addChar();
nextToken = TILDE;
break;
case '`':
addChar();
nextToken = GRAVE_ACCENT;
break;
case '\\':
addChar();
nextToken = BACKSLASH;
break;
default:
addChar();
nextToken = EOF;
break;
}
return nextToken;
}
/*****************************/
/* addChar = a function to add nextChar to lexeme */
void addChar()
{
if (lexLen <= 98)
{
lexeme[lexLen++] = nextChar;
lexeme[lexLen] = 0;
}
else
printf("Error - lexeme is too long \n");
}
/**********************************/
/* getChar- a function to get the next character of
input and determine its character class */
void getChar()
{
if ((nextChar = getc(in_fp)) != EOF)
{
if (isalpha(nextChar))
charClass = LETTER;
else if (isdigit(nextChar))
charClass = DIGIT;
else charClass = UNKNOWN;
}
else
charClass = EOF;
}
/********************************************/
/* getNonBlank - a function to call getChar until it
returns a non-whitespace character */
void getNonBlank()
{
while (isspace(nextChar))
getChar();
}
/*******************************/
/* lex - a simple lexical analyzer for arithmetic
expressions */
int lex()
{
lexLen = 0;
getNonBlank();
switch (charClass)
{
/*Parse identifiers */
case LETTER:
addChar();
getChar();
while (charClass == LETTER || charClass == DIGIT)
{
addChar();
getChar();
}
nextToken = IDENT;
break;
/*Parse integer literals and ?Floats?*/
case DIGIT:
addChar();
getChar();
while (charClass == DIGIT)
{
addChar();
getChar();
}
nextToken = INT_LIT;
break;
/*Parentheses and operators*/
case UNKNOWN:
lookup(nextChar);
getChar();
break;
/*EOF*/
case EOF:
nextToken = EOF;
lexeme[0] = 'E';
lexeme[1] = 'O';
lexeme[2] = 'F';
lexeme[3] = 0;
break;
}/*End of switch*/
printf("Next token is: %d, Next lexeme is %s\n",
nextToken, lexeme);
return nextToken;
} /*End of function lex*/
我在想，如果我使用了类似＆＃34; charClass.ch ==＆＃39;。＆＃39;＆＃34;在while语句中作为＆＃34; charClass == DIGIT＆＃34;的扩展。通过|| （或），但我想我可能会混淆另一种语言或做错了。我可能不会，但目前很难正确测试这个程序。
以下是我认为需要更改以获得浮动的特定部分：
/*Parse integer literals and ?Floats?*/
case DIGIT:
addChar();
getChar();
while (charClass == DIGIT)
{
addChar();
getChar();
}
nextToken = INT_LIT;
break;
答案 0 :(得分：1)
/*Parse integer literals and ?Floats?*/
case DIGIT:
addChar();
getChar();
while (charClass == DIGIT)
{
addChar();
getChar();
}
此时您已经知道nextChar是什么。如果它是一个点，请写一些代码来使用它以及所有后面的数字并将nextToken设置为FLOAT_LIT.否则会落到这一点：
nextToken = INT_LIT;
break;