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A simple Lexical analyzer
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
//void scaner();
int letter(char);
int digit(char);
char prog[80], token[8];
char ch;
int syn, p, m, n, sum;
char *rwtab[6] = {
"begin", "if", "then", "while", "do", "end"
};
int main(int argc, char const *argv[])
{
p = 0;
printf("\n please input string:\n");
do
{
ch = getchar();
prog[p++] = ch;
}while(ch!='#');
p = 0;
do
{ for (n = 0; n < 8; n++)
{
token[n] = NULL;
}
ch = prog[p++];
while(ch == ' ')
ch = prog[p++];
if (letter(ch))
{
m = 0;
while(letter(ch) || digit(ch))
{
token[m] = ch;
m++;
ch = prog[p++];
}
token[m++] = '\0';
p--;
syn = 10;
for (n = 0; n < 6; n++)
{
if (strcmp(token, rwtab[n]) == 0)
{
syn = n + 1;
break;
}
}
}
else if(digit(ch))
{
sum = 0;
while(digit(ch))
{
sum = sum * 10 + ch - '0';
ch = prog[p++];
}
p--;
syn = 11;
}
else
switch(ch)
{
case'<':
m = 0;
token[m++] = ch;
ch = prog[p++];
if (ch == '>')
{
syn = 21;
token[m++] = ch;
}
else if(ch == '=')
{
syn = 22;
token[m++] = ch;
}
else
{
syn = 20;
p--;
}
break;
case'>':
m = 0;
token[m++] = ch;
ch = prog[p++];
if (ch == '=')
{
syn = 24;
token[m++] = ch;
}
else
{
syn = 23;
p--;
}
break;
case':':
m = 0;
token[m++] = ch;
ch = prog[p++];
if (ch == '=')
{
syn = 18;
token[m++] = ch;
}
else
{
syn = 17;
p--;
}
break;
case'+': syn = 13; token[0] = ch; break;
case'-': syn = 14; token[0] = ch; break;
case'*': syn = 15; token[0] = ch; break;
case'/': syn = 16; token[0] = ch; break;
case';': syn = 26; token[0] = ch; break;
case'(': syn = 27; token[0] = ch; break;
case')': syn = 28; token[0] = ch; break;
case'#': syn = 0; token[0] = ch; break;
default:
syn = -1;
}
switch(syn)
{
case 11: printf("(%2d, %8d)\n", syn, sum); break;
case -1: printf("input error\n"); break;
default: printf("(%2d, %8s)\n", syn, token);
}
}while(syn != 0);
system("pause");
return 0;
}
/*
void scaner()
{
}
*/
int letter(char cha)
{
if(cha >= 'a' && cha <= 'z')
return 1;
else
return 0;
}
int digit(char cha)
{
if(cha >= '0' && cha <= '9')
return 1;
else
return 0;
}
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