hacktoberfest contribution

InfixToPostfixConversion.cpp

@@ -0,0 +1,147 @@
+/ C++ Program infix to postfix expression using stack (array) in data structure
+#include<iostream>
+#include<string>
+#define MAX 20
+using namespace std;
+
+char stk[20];
+int top=-1;
+// Push function here, inserts value in stack and increments stack top by 1
+void push(char oper)
+{
+    if(top==MAX-1)
+    {
+        cout<<"stackfull!!!!";
+    }
+
+    else
+    {
+        top++;
+        stk[top]=oper;
+    }
+}
+// Function to remove an item from stack.  It decreases top by 1
+char pop()
+{
+    char ch;
+    if(top==-1)
+    {
+        cout<<"stackempty!!!!";
+    }
+    else
+    {
+        ch=stk[top];
+        stk[top]='\0';
+        top--;
+        return(ch);
+    }
+    return 0;
+}
+int priority ( char alpha )
+{
+    if(alpha == '+' || alpha =='-')
+    {
+        return(1);
+    }
+
+    if(alpha == '*' || alpha =='/')
+    {
+        return(2);
+    }
+
+    if(alpha == '$')
+    {
+        return(3);
+    }
+
+    return 0;
+}
+string convert(string infix)
+{
+    int i=0;
+    string postfix = "";
+    while(infix[i]!='\0')
+    {
+        if(infix[i]>='a' && infix[i]<='z'|| infix[i]>='A'&& infix[i]<='Z')
+        {
+            postfix.insert(postfix.end(),infix[i]);
+            i++;
+        }
+        else if(infix[i]=='(' || infix[i]=='{'  || infix[i]=='[')
+        {
+            push(infix[i]);
+            i++;
+        }
+        else if(infix[i]==')' || infix[i]=='}'  || infix[i]==']')
+        {
+            if(infix[i]==')')
+            {
+                while(stk[top]!='(')
+                {               postfix.insert(postfix.end(),pop());
+                }
+                pop();
+                i++;
+            }
+            if(infix[i]==']')
+            {
+                while(stk[top]!='[')
+                {
+                    postfix.insert(postfix.end(),pop());
+                }
+                pop();
+                i++;
+            }
+
+            if(infix[i]=='}')
+            {
+                while(stk[top]!='{')
+                {
+                    postfix.insert(postfix.end(),pop());
+                }
+                pop();
+                i++;
+            }
+        }
+        else
+        {
+            if(top==-1)
+            {
+                push(infix[i]);
+                i++;
+            }
+
+            else if( priority(infix[i]) <= priority(stk[top])) {
+                postfix.insert(postfix.end(),pop());
+
+                while(priority(stk[top]) == priority(infix[i])){
+                    postfix.insert(postfix.end(),pop());
+                    if(top < 0) {
+                        break;
+                    }
+                }
+                push(infix[i]);
+                i++;
+            }
+            else if(priority(infix[i]) > priority(stk[top])) {
+                push(infix[i]);
+                i++;
+            }
+        }
+    }
+    while(top!=-1)
+    {
+        postfix.insert(postfix.end(),pop());
+    }
+    cout<<"The converted postfix string is : "<<postfix; //it will print postfix conversion
+    return postfix;
+}
+
+int main()
+{
+    int cont;
+    string infix, postfix;
+    cout<<"\nEnter the infix expression : "; //enter the expression
+    cin>>infix;
+    postfix = convert(infix);
+    return 0;
+}