Interview Questions And Answers 
-
Write a small lexical analyzer for expressions like “a*b” etc.
6,648 Views |
(6 votes, avg: 4.17)
Loading ...
Answers »
Our Sponsors
Our Sponsors
Write a small lexical analyzer for expressions like “a*b” etc.
6,648 Views | (6 votes, avg: 4.17)
Loading ...
int lex-a-star-b(char *s)
{
int i=0;
while(s[i]==’a')i++;
if((s[i]==’b')&&(s[i+1]==’ '))
return 1;
else
return 0;
}
#include <iostream.h>
bool is_astarb(char* s)
{
if (*s++ != ‘a’) return false;
while(*s++);
if (*—-s != ‘b’) return false;
return true;
}
void main()
{
char s1[] = “”;
char s2[] = “a”;
char s3[] = “b”;
char s4[] = “ba”;
char s5[] = “ab”;
char s6[] = “aajksdasb”;
cout << “s1 = ” << is_astarb(s1) << ‘n’;
cout << “s2 = ” << is_astarb(s2) << ‘n’;
cout << “s3 = ” << is_astarb(s3) << ‘n’;
cout << “s4 = ” << is_astarb(s4) << ‘n’;
cout << “s5 = ” << is_astarb(s5) << ‘n’;
cout << “s6 = ” << is_astarb(s6) << ‘n’;
}
I have programmed a lexical analyser(scanner).
I think it will work but there is some problems with the output.
/*
Implementation Of SCANNER
Grammar Ref: Appendix 4 ULLMAN
This program needs an input file named as ‘input.txt’ which contains the expressions(only)
This generates an output file named ‘output.txt’ & displays the output also in execution screen
*/
#include
#include
#include
#include
void main()
{
FILE *fp1,*fp2;
char str[100],sca[1000]=”";
int i,j,k,l,len,as,nscan;
clrscr();
fp1=fopen(”input.txt”,”r”);
fp2=fopen(”output.txt”,”w”);
if(fp1==NULL||fp2==NULL)
{
printf(”File or files could not be opened!\n”);
exit(0);
}
// printf(”Enter a string of expression:”);
// scanf(”%[^\n]s”,str);
// len=strlen(str);
// printf(”length=%d\n”,len);
do{
strcpy(str,”);
// printf(”str=%s”,str);
fscanf(fp1,”%s”,str);
len=strlen(str);
//printf(”Length=%d\t”,len);
k=0;
i=0;
nscan=0;
// printf(”String:%s\t”,str);
// getch();
do
{
as=toascii(str[i]);
if(isalpha(str[i]) && nscan!=1)
{
sca[k]=”;
}
else if(isdigit(str[i]))
{
sca[k++]=”;
}
else if(str[i]==’/’ && str[i+1]==’*')
{
// printf(” I am in comment segment”);
sca[k++]=’{';
i+=2;
// strcat(sca,”‘;
}
else if(str[i]==’('||str[i]==’)')
{
sca[k++]=”;
}
else if(str[i]==’;')
{
sca[k++]=”;
i++;
}
else if(nscan)
{
//strcpy(sca,”");
fprintf(fp2,”%s\n”,”Syntax error! Digits ending with Alphabet\n”
);
}
else
{
// printf(”Error occured!\nchar=%c%c%c”,str[i],str[i+1],str[i+2]);
// exit(0);
break;
}
sca[k++]=’ ‘;
// printf(”sca=%s\n”,sca);
}while(i
Leave an Answer/Comment