Added multiple C++ codes

Array in spiral order.cpp

@@ -0,0 +1,57 @@
+using namespace std;
+#include<iostream>
+
+int main()
+{
+    int a[20][20],row,col,i,j,top=0,bottom,left=0,right,k=1;
+
+    cout<<"\n Enter total number of rows :";
+    cin>>row;
+    cout<<"\n Enter total number of column :";
+    cin>>col;
+
+    right=col-1;
+    bottom=row-1;
+    for(i=0;i<row;i++)
+    {
+        cout<<"Enter "<<col<<" element of row "<<i+1<<" :";
+        for(j=0;j<col;j++)
+        {
+            cin>>a[i][j];
+        }
+    }
+
+    cout<<"\n Output:";
+
+    while(top<=bottom || right<=left)
+    {
+            for(i=left;i<=right;i++)
+            {
+                cout<<a[top][i]<<",";
+            }
+            top++;
+
+            for(i=top;i<=bottom;i++)
+            {
+                cout<<a[i][right]<<",";
+            }
+
+            right--;
+
+            for(i=right;i>=left;i--)
+            {
+                cout<<a[bottom][i]<<",";
+            }
+
+            bottom--;
+
+            for(i=bottom;i>=top;i--)
+            {
+                cout<<a[i][left]<<",";
+            }
+
+            left++;
+
+    }
+    return 0;
+}

BalancedParentheses.cpp

@@ -0,0 +1,38 @@
+using namespace std;
+#include<iostream>
+#include<stack>
+
+bool checkParentheses(string str){
+    stack<char> s;
+    for(int i=0; i<str.length();i++){
+        if(str[i]=='(' || str[i]=='{' || str[i]== '['){
+                s.push(str[i]);
+        }
+        else if(str[i]==')' || str[i]=='}' || str[i]== ']'){
+            if(s.empty())
+                return false;
+            else if(str[i]==')' && s.top()!= '(')
+                return false;
+            else if(str[i]=='}' && s.top()!= '{')
+                return false;
+            else if(str[i]==']' && s.top()!= '[')
+                return false;
+            else
+                s.pop();
+        }
+    }
+    if(s.empty())
+        return true;
+    return false;
+}
+int main()
+{
+    string str;
+    cin>>str;
+    if(checkParentheses(str)){
+        cout<<" Yes the parentheses are balanced";
+    }else{
+        cout<<" No, the parentheses are not balanced";
+    }
+    return 0;
+}

EvaluationPostfix.cpp

@@ -0,0 +1,34 @@
+//Evaluation of Postfix expression using stack
+using namespace std;
+#include<iostream>
+#include<stack>
+int evaluatePostfix(string str){
+    stack<int> S;
+    for(int i=0;i<str.length();i++){
+        if(isdigit(str[i])){
+            S.push(str[i]-'0');
+        }
+        else{
+            int op2 = S.top();
+            S.pop();
+            int op1 = S.top();
+            S.pop();
+            switch( str[i] ){
+                case '+' : S.push(op1+op2); break;
+                case '-' : S.push(op1-op2); break;
+                case '*' : S.push(op1*op2); break;
+                case '/' : S.push(op1/op2); break;
+                case '^' : S.push(op1^op2); break;
+            }
+        }
+    }
+    return S.top();
+}
+int main()
+{
+    string str;
+    cout<<"Enter the expression to be evaluated :";
+    cin>>str;
+    cout<<"Result after evaluation : "<<evaluatePostfix(str);
+    return 0;
+}

EvaluationPrefix.cpp

@@ -0,0 +1,35 @@
+//Evaluation of Prefix expression using stack
+using namespace std;
+#include<iostream>
+#include<stack>
+int evaluatePrefix(string str){
+    stack<int> S;
+    for(int i=str.length()-1;i>=0;i--){
+        if(isdigit(str[i])){
+            S.push(str[i]-'0');
+        }
+        else{
+            int op1 = S.top();
+            S.pop();
+            int op2 = S.top();
+            S.pop();
+            switch( str[i] ){
+                case '+' : S.push(op1+op2); break;
+                case '-' : S.push(op1-op2); break;
+                case '*' : S.push(op1*op2); break;
+                case '/' : S.push(op1/op2); break;
+                case '^' : S.push(op1^op2); break;
+            }
+        }
+    }
+    return S.top();
+}
+int main()
+{
+    string str;
+    cout<<"Enter the expression to be evaluated :";
+    cin>>str;
+    cout<<"Result after evaluation : "<<evaluatePrefix(str);
+    return 0;
+}
+

InfixToPostfix.cpp

@@ -0,0 +1,63 @@
+using namespace std;
+#include<iostream>
+#include<stack>
+
+int prec(char c){
+    if(c == '^')
+        return 3;
+    else if( c== '*' || c == '/')
+        return 2;
+    else if( c== '+' || c=='-')
+        return 1;
+    else{
+        return -1;
+    }
+}
+
+string postfix(string str){
+    string result="";
+    stack<char> S;
+    for(int i=0;i<str.length();i++){
+        if((str[i] >= 'a' && str[i] <= 'z') || (str[i] >= 'A' && str[i] <= 'Z') || (str[i] >= '0' && str[i] <= '9')){
+            result+=str[i];
+        }
+
+        else if(str[i]=='(')
+            S.push(str[i]);
+
+        else if(str[i]==')'){
+            while(S.top()!='('){
+                result +=S.top();
+                S.pop();
+            }
+            S.pop();
+        }
+        else{
+            if(S.empty())
+                S.push(str[i]);
+            else if(prec(str[i])>prec(S.top())){
+                S.push(str[i]);
+            }
+            else{
+                while(!S.empty() && (prec(str[i])<=prec(S.top()))){
+                    result+=S.top();
+                    S.pop();
+                }
+                S.push(str[i]);
+            }
+        }
+    }
+    while(!S.empty()){
+        result+=S.top();
+        S.pop();
+    }
+    return result;
+}
+
+int main(){
+    string str;
+    cout<<"enter the infix expression: ";
+    cin>>str;
+    cout<<"the postfix expression of the given infix expression is :"<< postfix(str);
+    return 0;
+}

ReverseALinkedList.cpp

@@ -0,0 +1,69 @@
+// reverse a linked list using stack
+
+#include<iostream>
+#include<stack>
+using namespace std;
+struct Node{
+    int data;
+    Node *next;
+};
+Node *head =NULL;
+
+void insertval(){
+    Node *temp= new Node();
+    int num;
+    cout<<"enter the value to be inserted:";
+    cin>>num;
+    temp->data= num;
+    temp->next=head;
+    head=temp;
+}
+void display( struct Node *temp){
+    cout<<temp->data<<" ";
+    if(temp->next!=NULL){
+        display(temp->next);
+    }
+}
+void reverseList( struct Node *temp)
+{
+    stack<struct Node*> S;
+    if(head==NULL){ return;}
+    while(temp!=NULL){
+        S.push(temp);
+        temp=temp->next;
+    }
+    temp=S.top();
+    head=temp;
+    S.pop();
+    while(!S.empty()){
+        temp->next = S.top();
+        S.pop();
+        temp=temp->next;
+    }
+    temp->next=NULL;
+    cout<<"Reversed list :";
+    display(head);
+}
+
+int main()
+{
+    int ch;
+    do{
+        cout<<"\n Enter your choice :";
+        cout<<"\n 1. Insert a new element ";
+        cout<<"\n 2. Display ";
+        cout<<"\n 3. Reverse the list";
+        cout<<"\n 4. Exit ";
+        cin>>ch;
+        if(ch==1){
+            insertval();
+        }
+        else if(ch==2){
+            display(head);
+        }
+        else if(ch==3){
+            reverseList(head);
+        }
+    }while(ch!=4);
+    return 0;
+}