Experiment No - 02

 Develop a lexical analyzer to recognize a few patterns in c

PROGRAM:

#include<stdio.h>

#include<conio.h>

#include<string.h>

void main()

{

FILE *fp;

int i,n;

char input[10];

char key[11][10]={"include","void","main()","int","char","float","if","else","while","do","for"};

char op[11][2]={"+","<",">","/","-","*","&","^","%","!","="};

char symbol[11][2]={",",")","(","?","{","}","[","]","#",";",":"};

clrscr();

fp=fopen("input.c","r");

fscanf(fp,"%s",input);

while(strcmp(input,"EOF")!=0)

{

for(i=0;i<11;i++)

{

if(strcmp(input,key[i])==0)

{

goto e;

}

}

for(i=0;i<11;i++)

{

if(strcmp(input,op[i])==0)

{

printf("<operator,%s>\n",input);

goto e;

}

}

for(i=0;i<11;i++)

{

if(strcmp(input,symbol[i])==0)

{

printf("<symbol,%s>\n",input);

goto e;

}

}

if((input[0]>='a' && input[0]<='z')||(input[0]>+'A'&& input [0]<='Z'))

{

n=strlen(input);

for(i=1;i<n;i++)

{

if((input[i]>='a'&&input[i]<='z')||(input[i]>='A'&&input[i]<='Z')||(input[i]>='0'&&input[i]<='9'))

continue;

else

{

printf("<\n Invalid identifiers,%s \n",input);

goto e;

}

}

if(i==n)

printf("<Identifiers,%s>\n",input);

}

else

printf("Invalid Identifiers\n");

e:

fscanf(fp,"%s",input);

}

getch();

}

INPUT:

void main()

{

int a,b;

float d;

d = a+b;

}

EOF

OUTPUT:

<symbol,{>

<Identifiers,a>

<symbol,;>

<Identifiers,b>

<symbol,;>

<Identifiers,double>

<Identifiers,c>

<symbol,;>

<Identifiers,d>

<symbol,;>

<Identifiers,c>

<operator,=>

<Identifiers,a>

<operator,+>

<Identifiers,b>

<symbol,;>

<symbol,}>