Notes

#include "../headerfiles/stack.h"
#include<math.h>
/*** AVAILABLE FUNCTIONS ***/
int isEmpty(Stack*);
void push(Stack*, int);
int pop(Stack*);
int peek(Stack*);


/*** YOUR FUNCTIONS ***/
//Write one function to convert infix expression to postifx expression using stack. Write another function to evaluate a postfix expression
int prec(char c) {
switch(c) {
case '(': return 0;
case '+':;
case '-': return 1;
case '*':;
case '/': return 2;
case '^': return 3;
}
}

void printPostfix(char* expr) {
Stack stk = {NULL};
for(int i = 0;expr[i] ; ++i) {
char c = expr[i];
//TODO: implement the algorithm to convert infix expression to postfix expression using stack based on the value of current input symbol c: if c is opening parenthesis, simply push it on to the stack, if c is an operand just print it, if c is a closing parenthesis pop and print all elements of stack until an opening parenthesis is encountered, otherwise c is an operator and we should pop and print all operators from the stack with equal or higher precedence than c before pushing c itself on the stack
if(c>='0' && c<='9')
printf(" %c ",c);
else if(c == '(')
push(&stk,c);
else if(c == ')'){
while(peek(&stk)!='(')
printf(" %c ",pop(&stk));
pop(&stk);
}
else{
while(!isEmpty(&stk) && prec(peek(&stk))>=prec(c))
printf(" %c ",pop(&stk));
push(&stk,c);
}
//TODO ENDS
}
//TODO: Empty the stack printing any values left in the stack
while(!isEmpty(&stk)){
printf("%c ",pop(&stk));
}
//TODO ENDS
printf("n");
}

int evalPostfix(char* pfx) {
Stack stk = {NULL};
for(int i = 0; pfx[i]; ++i) {
char c = pfx[i];
if(c>='0' && c<='9') push(&stk, c-'0');
else {
//TODO: Evaluate the postfix expression by popping two values from the stack and performing the operation based on the value of c and pushing the result back to the stack
int top = pop(&stk);
int secondTop = pop(&stk);
switch(c){
case '+': push(&stk,secondTop + top); break;
case '-': push(&stk,secondTop - top); break;
case '*': push(&stk,secondTop * top); break;
case '/': push(&stk,secondTop / top); break;
case '^': push(&stk,pow(secondTop,top)); break;
}//very cool
//TODO ENDS
}
}
return peek(&stk);
}

/*** MAIN DRIVER ***/
int main() {
char * expr = "2+5*(3^2-6)^(4+3*2)/9/3-8";
//ASSIGNMENTS
printPostfix(expr);
char * pfx = "2532^6-432*+^*9/3/+8-";
printf("%dn", evalPostfix(pfx));
}