int PostfixCheck(char equation[]) //This method checks either Postfix Equation is valid or not, incase of valid, it returns 1
{
int i;
Stack S;
S=createStack();
for(i=0;equation[i]!='\0';i++)
{
if(equation[i]!='+' && equation[i]!='-' && equation[i]=='/' && equation[i]=='*')
{
PushIntoStack(equation[i],S);
}
else if(equation[i]=='+' || equation[i]=='-' || equation[i]=='/' || equation[i]=='*')
{
Pop_Stack(S);
Pop_Stack(S);
PushIntoStack(equation[i],S);
}
else
PushIntoStack(equation[i],S);
}
Pop_Stack(S);
if(IsEmpty_Stack(S)==0)
return 1;
else
return 0;
}
void Calc(Linklist* operator, Linklist* numbers)
{
int num1 = Pop_Stack(numbers);
int num2 = Pop_Stack(numbers);
switch(Pop_Stack(operator))
{
case '+':
Push_Stack(numbers, num2 + num1);
break;
case '-':
Push_Stack(numbers, num2 - num1);
break;
case '*':
Push_Stack(numbers, num2 * num1);
break;
case '/':
Push_Stack(numbers, num2 / num1);
break;
default:
printf("error\n");
}
}
int main(int argc, const char* argv[])
{
Linklist operator;
Init_Stack(&operator);
Push_Stack(&operator, '#'); // avoid for empty stack..
Linklist numbers;
Init_Stack(&numbers);
char in = 0;
while(scanf("%c", &in) && in != '\n' && in != '\r')
{
// printf("in:%c\n", in);
if (in == ' ')
{
continue;
}
if (Is_Operator(in))
{
if (in == '+' || in == '-' || in == '*' || in == '/')
{
if (Operator_Level(Top_Stack(operator)) < Operator_Level(in)) // lower than in
{
// printf("compare: %c < %c success, push\n", Top_Stack(operator), in);
Push_Stack(&operator, in);
}
else
{
// printf("compare: %c >= %c success, calc\n", Top_Stack(operator), in);
Calc(&operator, &numbers);
Push_Stack(&operator, in);
}
}
else if (in == '(')
{
Push_Stack(&operator, in);
}
else if (in == ')')
{
while (Top_Stack(operator) != '(')
{
Calc(&operator, &numbers);
}
Pop_Stack(&operator);
}
else
{
printf("nothing:%c\n", in);
}
}
else
{
Push_Stack(&numbers, in - '0');
}
}
while(Top_Stack(operator) != '#')
{
Calc(&operator, &numbers);
}
printf("%d\n", Pop_Stack(&numbers));
return 0;
}
