#include <stdio.h>
#include <stdlib.h>
#include <string.h>
struct stack
{
int size;
int top;
char *arr;
};
int isFull(struct stack *ptr)
{
if (ptr->top == ptr->size - 1)
{
return 1;
}
else
{
return 0;
}
}
int isEmpty(struct stack *ptr)
{
if (ptr->top == -1)
{
return 1;
}
else
{
return 0;
}
}
void push(struct stack *ptr, char val)
{
if (isFull(ptr))
{
printf("Stack Overflow....");
}
else
{
ptr->top++;
ptr->arr[ptr->top] = val;
}
}
char pop(struct stack *ptr)
{
if (isEmpty(ptr))
{
printf("Stack Underflow...");
return -11;
}
else
{
char val = ptr->arr[ptr->top];
ptr->top--;
return val;
}
}
int stackTop(struct stack *ptr)
{
return ptr->arr[ptr->top];
}
int precedence(char ch)
{
if (ch == '*' || ch == '/')
{
return 3;
}
else if (ch == '+' || ch == '-')
{
return 2;
}
else
{
return 0;
}
}
int isOperator(char ch)
{
if (ch == '+' || ch == '-' || ch == '*' || ch == '/')
{
return 1;
}
else
{
return 0;
}
}
char *infixToPostfix(char *infix)
{
struct stack *sp = (struct stack *)malloc(sizeof(struct stack));
sp->size = 100;
sp->top = -1;
sp->arr = (char *)malloc(sp->size * sizeof(char));
char *postfix = (char *)malloc((strlen(infix) + 1) * sizeof(char));
int i = 0;
int j = 0;
while (infix[i])
{
if (!isOperator(infix[i]))
{
postfix[j] = infix[i];
j++;
i++;
}
else
{
if (precedence(infix[i]) > precedence(stackTop(sp)))
{
push(sp, infix[i]);
i++;
}
else
{
postfix[j] = pop(sp);
j++;
}
}
}
while (!isEmpty(sp))
{
postfix[j] = pop(sp);
j++;
}
postfix[j] = '\0';
return postfix;
}
int main()
{
char a[100];
printf("Enter A infix Experession (Without Space) : ");
scanf("%s",&a); // **This is also be written as : gets(a);
char *infix = a;//"x-y/z-k*d";
printf("Postfix Expression is : %s", infixToPostfix(infix));
return 0;
}
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