Page 71 - DCAP605_ADVANCED_DATA_STRUCTURE_AND_ALGORITHMS

Advanced Data Structure and Algorithms

Notes char top_ch;

stk stack;
initStack(&stack); /* initialise stack */
get_infix(infix); /* get infix expression from user */
length = strlen(infix);
if ( length ) /* if strlen if infix is more than zero */
{
push(&stack, ‘(‘);
strcat(infix, “)”);
length++;
for ( i=0; i<length; i++ )
{
if ( isdigit(infix[i]) ) /* if current operator in infix is digit */
{
postfix[j++] = infix[i];
}
else if ( infix[i] == ‘(‘ ) /* if current operator in infix is
left parenthesis */
{
push(&stack, ‘(‘);
}
else if ( isOperator(infix[i]) ) /* if current operator is operator */
{
while(1)
{
top_ch = stackTop(&stack); /* get tos */
if ( top_ch == ‘\0’ ) /* no stack left */
{
printf(“\nInvalid infix expression\n”);
exit(1);
}
else
{
if ( isOperator(top_ch) )
{
if ( pred_level(top_ch) >= pred_level(infix[i]) )
postfix[j++] = pop(&stack);
else
break;
}
else

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