Dynamic Memory Allocation
#include <stdio.h>
#include <stdlib.h>
int main()
{
// This pointer will hold the
// base address of the block created
int *ptr;
int n, i;
// Get the number of elements for the array
printf("Enter number of elements:");
scanf("%d", &n);
printf("Entered number of elements: %d\n", n);
// Dynamically allocate memory using malloc()
// Since the size of int is 4 bytes, this statement will allocate n*4 bytes of memory. And, the pointer ptr holds the address of the first byte in the allocated memory.
ptr = (int *)malloc(n * sizeof(int));
// Dynamically allocate memory using calloc()
// This statement allocates contiguous space in memory for n elements each with the size of the float.
ptr = (float *)calloc(n, sizeof(float));
// Dynamically re-allocate memory using realloc()
ptr = realloc(ptr, n * sizeof(int));
// Check if the memory has been successfully
// allocated by malloc/calloc or not
if (ptr == NULL)
{
printf("Memory not allocated.\n");
exit(0);
}
else
{
// Memory has been successfully allocated
printf("Memory successfully allocated using malloc.\n");
// Get the elements of the array
for (i = 0; i < n; ++i)
{
ptr[i] = i + 1;
}
// Print the elements of the array
printf("The elements of the array are: ");
for (i = 0; i < n; ++i)
{
printf("%d, ", ptr[i]);
}
// Free the memory
free(ptr);
printf("Malloc Memory successfully freed.\n");
}
return 0;
}Array Operations
#include <stdio.h>
#include <stdlib.h>
#define MAX 20
int arr[MAX];
int pos, elem, n;
void create();
void display();
void insert();
void delete();
void create()
{
int i;
printf("Enter the size of the array : ");
scanf("%d", &n);
printf("Enter the elements of the array : ");
for (i = 0; i < n; i++)
scanf("%d", &arr[i]);
}
void display()
{
int i;
if (n == 0)
{
printf("Array is empty ");
return;
}
printf("Array elements are : ");
for (i = 0; i < n; i++)
printf("%d ", arr[i]);
printf(" ");
}
void insert()
{
int i;
if (n == MAX)
{
printf("Array is full ");
return;
}
printf("Enter the position for the new element : ");
scanf("%d", &pos);
printf("Enter the element to be inserted : ");
scanf("%d", &elem);
for (i = n - 1; i >= pos; i--)
arr[i + 1] = arr[i];
arr[pos] = elem;
n = n + 1;
}
void delete()
{
int i;
printf("Enter the position of the element to be deleted : ");
scanf("%d", &pos);
elem = arr[pos];
printf("Element deleted is : %d ", elem);
for (i = pos; i <= n - 1; i++)
arr[i] = arr[i + 1];
n = n - 1;
}
int main()
{
int choice;
int pos = 1;
while (1)
{
printf("\n1.Create an array ");
printf("\n2.Display the array ");
printf("\n3.Insert an element ");
printf("\n4.Delete an element ");
printf("\n5.Exit ");
printf("\nEnter your choice : ");
scanf("%d", &choice);
switch (choice)
{
case 1:
create();
break;
case 2:
display();
break;
case 3:
insert();
break;
case 4:
delete ();
break;
case 5:
exit(1);
default:
printf("Wrong choice ");
}
}
}Stacks Array
// Write a c program to implement STACK using array
// STACK of Integers (Array Implementation of Stack with maximum
// size MAX)
// a) Push an Element on to Stack
// b) Pop an Element from Stack
// c) Demonstrate how Stack can be used to check Palindrome
// d) Demonstrate Overflow and Underflow situations on Stack
// e) Display the status of Stack
// f) Exit
// Support the program with appropriate functions for each of the
// above operations
#include <stdio.h>
#include <stdlib.h>
#define MAX 5
int stack[MAX];
int top = -1;
void push(int x)
{
if (top == MAX - 1)
printf("Stack Overflow ");
else
{
top = top + 1;
stack[top] = x;
}
}
int pop()
{
int x;
if (top == -1)
printf("Stack Underflow ");
else
{
x = stack[top];
top = top - 1;
return x;
}
}
void display()
{
int i;
if (top == -1)
printf("Stack is empty ");
else
{
printf("Stack elements are : ");
for (i = top; i >= 0; i--)
printf("%d ", stack[i]);
}
}
void check_palindrome()
{
int i, j, flag = 0;
char str[20];
printf("Enter the string : ");
scanf("%s", str);
for (i = 0; str[i] != '\0'; i++)
push(str[i]);
for (j = 0; str[j] != '\0'; j++)
{
if (str[j] != pop()) // str[j] is first element of string and pop() is last element of string
{
flag = 1; // if first and last elements are not same then flag is set to 1
break;
}
}
if (flag == 1)
printf("String is not a palindrome ");
else
printf("String is a palindrome ");
}
int main()
{
int choice, x;
while (1)
{
printf("\n1.Push ");
printf("\n2.Pop ");
printf("\n3.Display ");
printf("\n4.Quit ");
printf("\n5.Check Palindrome ");
printf("\nEnter your choice : ");
scanf("%d", &choice);
switch (choice)
{
case 1:
printf("Enter the element to be pushed : ");
scanf("%d", &x);
push(x);
break;
case 2:
x = pop();
printf("Popped element is : %d", x);
break;
case 3:
display();
break;
case 4:
exit(1);
case 5:
check_palindrome();
break;
default:
printf("Wrong choice ");
}
}
}Infix Expression to Postfix Expression
#include <stdio.h>
#include <ctype.h>
char stack[100];
int top = -1;
void push(char x)
{
stack[++top] = x;
}
char pop()
{
if (top == -1)
return -1;
else
return stack[top--];
}
int priority(char x)
{
if (x == '(')
return 0;
if (x == '+' || x == '-')
return 1;
if (x == '*' || x == '/')
return 2;
return 0;
}
int main()
{
char exp[100];
char *e, x;
printf("Enter the expression : ");
scanf("%s", exp);
printf("\n");
e = exp; // e is a pointer to expression
while (*e != '\0')
{
if (isalnum(*e))
printf("%c ", *e);
else if (*e == '(')
push(*e);
else if (*e == ')')
{
while ((x = pop()) != '(') // pop until ( is encountered
printf("%c ", x);
}
else
{
while (priority(stack[top]) >= priority(*e)) // pop until priority of stack top is less than that of *e
printf("%c ", pop());
push(*e);
}
e++;
}
while (top != -1)
{
printf("%c ", pop()); // pop until stack is empty
}
return 0;
}Infix Expression to Prefix Expression
#include <stdio.h>
#include <ctype.h>
char stack[100];
int top = -1;
void push(char x)
{
stack[++top] = x;
}
char pop()
{
if (top == -1)
return -1;
else
return stack[top--];
}
int priority(char x)
{
if (x == '(')
return 0;
if (x == '+' || x == '-')
return 1;
if (x == '*' || x == '/')
return 2;
if (x == '^')
return 3;
return 0;
}
void reverse(char *exp)
{
int size = strlen(exp);
int j = size, i = 0;
char temp[size];
temp[j--] = '\0';
while (exp[i] != '\0')
{
temp[j] = exp[i];
j--;
i++;
}
strcpy(exp, temp);
}
void brackets(char *exp)
{
int i = 0;
while (exp[i] != '\0')
{
if (exp[i] == '(')
exp[i] = ')';
else if (exp[i] == ')')
exp[i] = '(';
i++;
}
}
int main()
{
char exp[100];
char *e, x;
printf("Enter the expression : ");
scanf("%s", exp);
reverse(exp);
brackets(exp);
printf("\n");
e = exp; // e is a pointer to expression
while (*e != '\0')
{
if (isalnum(*e))
printf("%c ", *e);
else if (*e == '(')
push(*e);
else if (*e == ')')
{
while ((x = pop()) != '(') // pop until ( is encountered
printf("%c ", x);
}
else
{
while (priority(stack[top]) >= priority(*e))
printf("%c ", pop());
push(*e);
}
e++;
}
while (top != -1)
{
printf("%c ", pop());
}
printf("\n");
return 0;
}Postfix Evaluation
int stack[20];
int top = -1;
void push(int x)
{
stack[++top] = x;
}
int pop()
{
return stack[top--];
}
int main()
{
char exp[20];
char *e;
int n1, n2, n3, num;
printf("Enter the expression :: ");
scanf("%s", exp);
e = exp;
while (*e != '\0')
{
if (isdigit(*e))
{
num = *e - 48; // converting char to int
push(num);
}
else
{
n1 = pop();
n2 = pop();
switch (*e)
{
case '+':
{
n3 = n2 + n1;
break;
}
case '-':
{
n3 = n2 - n1;
break;
}
case '*':
{
n3 = n2 * n3;
break;
}
case '/':
{
n3 = n2 / n1;
break;
}
}
push(n3);
}
e++;
}
printf("\nThe result of expression %s = %d\n\n", exp, pop());
return 0;
}Parentheses Checker
#include <stdio.h>
#include <string.h>
#define MAX 10
int top = -1;
int stk[MAX];
void push(char);
char pop();
void main()
{
char exp[MAX], temp;
int i, flag = 1;
printf("Enter an expression : ");
gets(exp);
for (i = 0; i < strlen(exp); i++)
{
if (exp[i] == '(' || exp[i] == '{' || exp[i] == '[')
push(exp[i]);
if (exp[i] == ')' || exp[i] == '}' || exp[i] == ']')
if (top == -1)
flag = 0;
else
{
temp = pop();
if (exp[i] == ')' && (temp == '{' || temp == '['))
flag = 0;
if (exp[i] == '}' && (temp == '(' || temp == '['))
flag = 0;
if (exp[i] == ']' && (temp == '(' || temp == '{'))
flag = 0;
}
}
if (top >= 0)
flag = 0;
if (flag == 1)
printf("\n Valid expression");
else
printf("\n Invalid expression");
}
void push(char c)
{
if (top == (MAX - 1))
printf("Stack Overflow\n");
else
{
top = top + 1;
stk[top] = c;
}
}
char pop()
{
if (top == -1)
printf("\n Stack Underflow");
else
return (stk[top--]);
}Queue using Array
#include <stdio.h>
#include <stdlib.h>
#define MAX 5
int queue[MAX];
int front = -1;
int rear = -1;
void insert();
void delete();
void display();
void insert()
{
int add_item;
if (rear == MAX - 1)
printf("Queue Overflow ");
else
{
if (front == -1) //If queue is initially empty
front = 0;
printf("Inset the element in queue : ");
scanf("%d", &add_item);
rear = rear + 1;
queue[rear] = add_item;
}
}
void delete()
{
if (front == -1 || front > rear)
{
printf("Queue Underflow ");
return;
}
else
{
printf("Element deleted from queue is : %d", queue[front]);
front = front + 1;
}
}
void display()
{
int i;
if (front == -1)
printf("Queue is empty ");
else
{
printf("Queue is : ");
for (i = front; i <= rear; i++)
printf("%d ", queue[i]);
printf("\n");
}
}
int main()
{
int choice;
while (1)
{
printf("\n1.Insert");
printf("\n2.Delete");
printf("\n3.Display");
printf("\n4.Quit ");
printf("\nEnter your choice : ");
scanf("%d", &choice);
switch (choice)
{
case 1:
insert();
break;
case 2:
delete ();
break;
case 3:
display();
break;
case 4:
exit(1);
default:
printf("Wrong choice ");
}
}
}Credits to Reema Thareja Book
If any of the above code is not working or you have a better code to contribute, feel free to create a pull request.