Program:

In this program - first, we are declaring a variable named num and assigning any value in it. Since we cannot predict a valid memory address. So here, we will print the memory address of num and then, we will read it from the user and print its value.

#include <stdio.h>

int main(void) 
{

	int num = 123;
	int *ptr; //to store memory address

	printf("Memory address of num = %p\n", &num);

	printf("Now, read/input the  memory address: ");
	scanf ("%p", &ptr);

	printf("Memory address is: %p and its value is: %d\n", ptr, *ptr);

	return 0;
}

Output

Memory address of num = 0x7ffc505d4a44
Now, read/input the  memory address: 7ffc505d4a44
Memory address is: 0x7ffc505d4a44 and its value is: 123 

Explanation:

In this program, we declared an unsigned int variable named num and assigned the variable with the value 123.

Then, we print the value of num by using "%p" format specifier – it will print the memory address of num – which is 0x7ffc505d4a44.

Then, we prompt a message "Now, read/input the memory address: " to take input the memory address – we input the same memory address which was the memory address of num. The input value is 7ffc505d4a44. And stored the memory address to a pointer variable ptr. (you must know that only pointer variable can store the memory addresses. Read more: pointers in C language).

Note: While input, "0x" is not required.

And finally, when we print the value using the pointer variable ptr. The value is 123.