Program for implementation of non recursive predictive parser?

Answer 1

Aim:

Parse the following grammar.

E --> E + T / T

T --> T * F / F

F --> ( E ) / id

Program:

#include

#include

#include

#include

void err(const char* s)

{

perror(s);

exit(0);

}

int factor()

{

int val,i;

char ch[0];

scanf("%s",ch);

switch(ch[0])

{

case '(':

val=expr();

scanf("%s",ch);

if(ch[0]!=')')

err("Missing closing paranthesis in factor.");

break;

default :{

for(i=0;i

{

if((ch[i]>'0')&&(ch[i]<='9'))

continue;

else

err("Illegal character sequence in place of factor.");

}

val=atoi(ch);

}

}

return val;

}

int term()

{

int val;

char ch[10];

val=factor();

while(1)

{

scanf("%s",ch);

if(ch[0]=='*')

{

val=val*factor();

}

else

break;

}

ungetc(ch[0],stdin);

return val;

}

int expr()

{

int val;

char ch[10];

val=term();

while(1)

{

scanf("%s",ch);

if(ch[0]=='+')

val=val+term();

else

break;

}

ungetc(ch[0],stdin);

return val;

}

main()

{

printf("\nEnter the expression: ");

printf("\n Result: %d\n",expr());

}

Output:

nn@linuxmint ~ $ gcc rec.c

nn@linuxmint ~ $ ./a.out

Enter the expression: 5 * ( 3 + 1 )

;

Result: 20

nn@linuxmint ~ $