Page 97 - DCAP605_ADVANCED_DATA_STRUCTURE_AND_ALGORITHMS

Advanced Data Structure and Algorithms

Notes
}
printf( “\tS pushing %c...\n”, op );
sPush( s, op );
break;
}
}
}
bool isop( char op ) {
/*
* is op an operator?
*/
return (getIndex(op) != -1);
}
char *in2pre( char *str ) { /*
* returns valid infix expr in str to prefix.
*/
char *sptr;
queue q = {NULL};
stack s = NULL;
char *res = (char *)malloc( N*sizeof(char) );
char *resptr = res;
tptr = t;
for( sptr=str+strlen(str)-1; sptr!=str-1; -sptr ) {
printf( “processing %c tptr-t=%d...\n”, *sptr, tptr-t );
if( isalpha(*sptr) ) // if operand.
qPush( &q, *sptr );
else if( isop(*sptr) ) // if valid operator.
processOp( *sptr, &q, &s );
else if( isspace(*sptr) ) // if whitespace.
;
else {
fprintf( stderr, “ERROR:invalid char %c.\n”, *sptr );
return “”;
}
}
while( !qEmpty(&q) ) {
*tptr++ = qPop(&q);
printf( “\tQ popping %c...\n”, *(tptr-1) );
}
while( !sEmpty(&s) ) {
*tptr++ = sPop(&s);
printf( “\tS popping %c...\n”, *(tptr-1) );
Contd...
}

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