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Interview Questions/README.MD

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+# Interview Questions and Answers
+
+| Sl no. | Question | Answer link | Language | Contributor |
+|---|---|---|---|---|
+| 1 | Implementing **Stack** using **Array** and **Linked List** | [code here](https://github.com/nitinkumar30/basicprograms/blob/master/Interview%20Questions/implementing_stack_using_array_and_linked_list.c) | C | [Nitin Kumar](https://github.com/nitinkumar30/)
+
+
+# Repo contributed by
+
+[Nitin Kumar](https://github.com/nitinkumar30/)

Interview Questions/implementing_stack_using_array_and_linked_list.c

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+// Implementing stack using Array in C language
+
+// -------------------------------------------------------
+
+#include<stdio.h>
+#include<stdlib.h>
+
+struct Stack{
+    int size;
+    int top;
+    int *arr;
+};
+
+// ---- operations to perform :
+// isEmpty-
+// isFull-
+// push-
+// pop-
+// peek-
+// stackTop-
+// stackBottom-
+
+// -------------------------------------
+
+int isEmpty(struct Stack * ptr){
+    if(ptr->top == -1)
+        return 1;
+    else
+        return 0;
+}
+// -------------------------------------
+
+int isFull(struct Stack * ptr){
+    if(ptr->top == ptr->size-1)
+        return 1;
+    else
+        return 0;
+}
+// -------------------------------------
+
+void push(struct Stack *ptr, int data){
+    if(isFull(ptr)){
+        printf("Stack Overflow for data %d \n", data);
+    }
+    else{
+        ptr->top+=1;
+        ptr->arr[ptr->top] = data;
+    }
+}
+// -------------------------------------
+
+int pop(struct Stack *ptr){
+    if(isEmpty(ptr))
+        printf("Stack Underflow");
+    else{
+        int p = ptr->arr[ptr->top];
+        ptr->top-=1;
+        return p;
+    }
+}
+// -------------------------------------
+
+int peek(struct Stack *ptr, int i){
+    int arrInd = ptr->top-i+1;
+    if(arrInd <= -1)
+        printf("Not valid position.");
+    else
+        return ptr->arr[arrInd];
+    return -1;
+}
+// -------------------------------------
+
+int stackTop(struct Stack *ptr){
+    return ptr->arr[ptr->top];
+}
+// -------------------------------------
+
+int stackBottom(struct Stack *ptr){
+    return ptr->arr[0];
+}
+// -------------------------------------
+
+int main(){
+    struct Stack *s = (struct Stack *)malloc(sizeof(struct Stack));
+    s->size=10;
+    s->top=-1;
+    s->arr=(int *)malloc(s->size*sizeof(int));
+
+    printf("Before pushing: Full %d\n",isFull(s));
+    printf("Before pushing: Empty %d\n",isEmpty(s));
+
+    push(s, 1);
+    push(s, 2);
+    push(s, 3);
+    push(s, 4);
+    push(s, 5);
+    push(s, 6);
+    push(s, 7);
+    push(s, 8);
+    push(s, 9);
+    push(s, 10);
+    push(s, 11);
+    push(s, 12);
+    push(s, 13);
+
+    printf("After pushing: Full %d\n",isFull(s));
+    printf("After pushing: Empty %d\n",isEmpty(s));
+
+    printf("\n----------------------\n");
+    printf("Peeking through stack\n");
+    for(int j=1;j<s->top+2;j++){
+        printf("The value at position %d is %d\n", j, peek(s, j));
+    }
+
+    printf("\nPopped %d from stack", pop(s));
+    printf("\nPopped %d from stack", pop(s));
+    printf("\nPopped %d from stack", pop(s));
+    printf("\nPopped %d from stack\n\n", pop(s));
+
+    printf("After popping: Full %d\n",isFull(s));
+    printf("After popping: Empty %d\n",isEmpty(s));
+
+    printf("\n----------------------\n");
+    printf("Peeking through stack\n");
+    for(int j=1;j<s->top+2;j++){
+        printf("The value at position %d is %d\n", j, peek(s, j));
+    }
+
+    printf("\nStack at top now is %d", stackTop(s));
+    printf("\nStack at bottom now is %d", stackBottom(s));
+
+    return 0;
+}
+
+// ------------------------------------------------------------------------------------------------------
+
+// Implementing Stack using Linked List in C language
+
+#include<stdio.h>
+#include<stdlib.h>
+
+struct Node{
+    int data;
+    struct Node *next;
+};
+
+// isEmpty
+// isFull
+// push
+// pop
+
+struct Node * top = NULL;
+
+void traverseLinkedList(struct Node *ptr){
+    while(ptr!=NULL){
+        printf("Element is %d\n", ptr->data);
+        ptr=ptr->next;
+    }
+}
+
+int isEmpty(struct Node *top){
+    if(top == NULL)
+        return 1;
+    else
+        return 0;
+}
+
+int isFull(struct Node *top){
+    struct Node *n = (struct Node*)malloc(sizeof(struct Node));
+    if (n==NULL)
+        return 1;
+    else
+        return 0;
+}
+
+int pop(struct Node *tp){
+    if(isEmpty(top))
+        printf("Stack Underflow");
+    else{
+        struct Node *p = tp;
+        top = (tp) -> next;
+        int m=p->data;
+        free(p);
+        return m;
+    }
+}
+
+struct Node *push(struct Node *top, int x){
+    if (isFull(top))
+        return 1;
+    else{
+        struct Node *pr = (struct Node*)malloc(sizeof(struct Node));
+        pr->data = x;
+        pr->next = top;
+        top = pr;
+        return top;
+    }
+}
+
+int main(){
+    top = push(top, 3);
+    top = push(top, 6);
+    top = push(top, 11);
+    top = push(top, 23);
+    top = push(top, 47);
+
+    traverseLinkedList(top);
+
+    int element=pop(top);
+    printf("Popped element is %d \n", element);
+
+    traverseLinkedList(top);
+
+    return 0;
+
+}
+
+