From 710c18a36b3e6294bb0e21dba976057b1a964d3f Mon Sep 17 00:00:00 2001
From: Apoorva77 <apoorvaprabhur@gmail.com>
Date: Sun, 17 Oct 2021 19:24:36 +0530
Subject: [PATCH] Create Infix_expression.c

---
 Infix_expression.c | 138 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 138 insertions(+)
 create mode 100644 Infix_expression.c

diff --git a/Infix_expression.c b/Infix_expression.c
new file mode 100644
index 0000000..83b14bc
--- /dev/null
+++ b/Infix_expression.c
@@ -0,0 +1,138 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+#include<math.h>
+#include<ctype.h>
+#include<string.h>
+#define max 100
+#define TRUE 1
+#define FALSE 0
+
+struct stack
+{
+     int top;
+     char items[max];
+};
+
+struct stack s;
+char infix[max],postfix[max];
+int pos=0;
+void convert();
+void push(char);
+char pop();
+int precedence(char);
+int f=0;
+int empty();
+int stackfull();
+
+int main()
+{
+     s.top=-1;
+     printf("Enter the infix expression\n");
+     gets(infix);
+     convert();
+     if(f==0)
+     {
+         printf("The postfix expression is\n");
+         puts(postfix);
+     }
+     return 0;
+}
+
+void convert()
+{
+     if(infix[0]=='\0') { f=1; printf("Invalid input\n"); return; }
+     int i;
+     char symbol,temp;
+     for(i=0; infix[i]!='\0';i++)
+     {
+         symbol=infix[i];
+         switch(symbol)
+        {
+             case '(': push(symbol);
+             break;
+             case ')': while((temp=pop())!='(')
+             postfix[pos++]=temp;
+             break;
+             case '+':
+             case '-':
+             case '*':
+             case '/':
+             case '$':
+                        while(!empty()&&precedence(s.items[s.top])>=precedence(symbol)&&precedence(symbol)!=-1)
+                         {
+                             temp=pop();
+                             postfix[pos++]=temp;
+                         }
+                         push(symbol);
+                         break;
+            default: if(!isalpha(symbol))
+                     {
+                         printf("Invalid input\n");
+                         f=1;
+                         return;
+                     }
+                     else
+                     {
+                         postfix[pos++]=symbol;
+                         break;
+                     }
+         }
+     }
+     while(!empty())
+     {
+         temp=pop();
+         postfix[pos++]=temp;
+     }
+}
+
+void push(char ele)
+{
+     if(stackfull())
+        printf("Stack is full\n");
+     else
+        s.items[++s.top]=ele;
+}
+
+char pop()
+{
+     if(empty())
+     {
+         printf("Stack is empty\n");
+         exit(0);
+     }
+     else
+        return(s.items[s.top--]);
+}
+
+int stackfull()
+{
+     if(s.top==max-1)
+        return TRUE;
+     else
+        return FALSE;
+}
+
+int empty()
+{
+     if(s.top==-1)
+        return TRUE;
+     else
+        return FALSE;
+}
+
+int precedence(char symbol)
+{
+     switch(symbol)
+     {
+         case '$':return 3;
+         case '*':
+         case '/':return 2;
+         case '+':
+         case '-':return 1;
+         case '(':
+         case ')':return(0);
+         default: printf("Invalid input\n");
+         return -1;
+     }
+}