EvaluareExpresie

#include <iostream>
#include <cstdio>
#include <cstring>
#include <ctype.h>
#include <cmath>
#define MAX 100
#define EMPTY -1
using namespace std;
struct stack
{
	char data[MAX];
	long long int top;
};

int isempty(struct stack *s)
{
	return (s->top==EMPTY)?1:0;
}

void emptystack(struct stack* s)
{
	s->top=EMPTY;
}

void push(struct stack* s,int item)
{
	if(s->top==(MAX-1))
	{
		printf("\nSTACK FULL");
	}
	else
	{
		++s->top;
		s->data[s->top]=item;
	}
}

char pop(struct stack* s)
{
	char ret=(char)EMPTY;
	if(!isempty(s))
	{
		ret=s->data[s->top];
		--s->top;
	}
	return ret;
}

void display(struct stack s)
{
	while(s.top != EMPTY)
	{
		printf("\n%d",s.data[s.top]);
		s.top--;
	}
}

int isoperator(char e)
{
	if(e=='+'||e=='-'||e=='*'||e=='^')
		return 1;
	else
		return 0;
}


int priority(char e)
{
	int pri=0;
    if(e=='^')
        pri=3;
    else
        if(e=='*')
            pri=2;
        else
            if(e=='+'||e=='-')
                pri=1;
	return pri;
}

void infix2postfix(char* infix, char * postfix, int insertspace)
{
	char *i,*p;
	struct stack X;
	char n1;
	emptystack(&X);
	i=&infix[0];
	p=&postfix[0];
	while(*i)
	{
		while(*i==' '||*i=='\t')
		{
			i++;
		}
		if(isdigit(*i)||isalpha(*i))
		{
			while(isdigit(*i)||isalpha(*i))
			{
				*p=*i;
				p++;
				i++;
			}
			/*SPACE CODE*/
			if(insertspace)
			{
				*p=' ';
				p++;
			}
			/*END SPACE CODE*/
		}
		if(*i=='(' )
		{
			push(&X,*i);
			i++;
		}
		if(*i==')')
		{
			n1=pop(&X);
			while(n1!='(' )
			{
				*p=n1;
				p++;
				/*SPACE CODE*/
				if(insertspace)
				{
					*p=' ';
					p++;
				}
				/*END SPACE CODE*/
				n1=pop(&X);
			}
			i++;
		}
		if(isoperator(*i))
		{
			if(isempty(&X))
				push(&X,*i);
			else
			{
				n1=pop(&X);
				while(priority(n1)>=priority(*i))
				{
					*p=n1;
					p++;
					/*SPACE CODE*/
					if(insertspace)
					{
						*p =' ';
						p++;
					}
					/*END SPACE CODE*/
					n1=pop(&X);
				}
				push(&X,n1);
				push(&X,*i);
			}
			i++;
		}
	}
	while(!isempty(&X))
	{
		n1=pop(&X);
		*p=n1;
		p++;
		/*SPACE CODE*/
		if(insertspace)
		{
			*p=' ';
			p++;
		}
		/// END SPACE CODE
	}
	*p ='\0';
}

long long int evaluate(char *postfix)
{
	char *p;
	long long int S[100];
	int varf=0;
	long long int nr=0,op1,op2,result;
	p=&postfix[0]; /// In p avem expresia in forma postfixata
	///cout<<p<<"I"<<endl;
	while(*p!='\0') /// Cat timp n-am ajuns la sfarsitul expresiei
	{
	   /// removes tabs and spaces
		if(*p==' '||*p=='\t')
		{
			p++;
		}
	  /// if is digit
		if(isdigit(*p))
		{
			nr=(long long int)(*p-48);
			p++;
			while(isdigit(*p))
                nr=nr*10+(*p-48),++p;
			S[++varf]=nr;
		}
		else
		{
		   /// it is an operator
			if(varf)
                op1=S[varf--];
			if(varf)
                op2=S[varf--];
			///cout<<"OPERATIA: "<<op1<<' '<<*p<<' '<<op2<<endl;
			///if(*p!='+'||*p!='-'||*p!='*'||*p!='^')
			switch(*p)
			{
				case '+':
					result=op2+op1;
					break;

				case '-':
					result=op2-op1;
					break;

				case '^':
					result=(long long int)pow(op2,op1);
					break;

				case '*':
					result=op2*op1;
					break;

				default:
					printf("\nInvalid Operator");
					return 0;
			}
			S[++varf]=result;
		}
		p++;
	}
	result=S[varf];
	return result;
}

int main()
{
	char in[50]={0},post[100]={0};
	FILE *f=fopen("evaluareexpresie.in","r");
	fscanf(f,"%s",in);
	fclose(f);
	///cout<<"S= "<<in<<endl;
	infix2postfix(in,post,1);
	FILE *g=fopen("evaluareexpresie.out","w");
	unsigned int L=strlen(post);
    while(post[L-1]!='+'&&post[L-1]!='-'&&post[L-1]!='*'&&post[L-1]!='^')
        --L;
    post[L]='\0';
	fprintf(g,"%s\n",post);
	fprintf(f,"%lld\n",evaluate(post));
	fclose(g);
	return 0;
}