Explaination:
This program prints "Hello world" using the inner printf() function, which returns the number of characters printed (11 in this case). The outer printf() then prints 11 as the result.

// Program to print value of a variable using pointer
#include<stdio.h>
int main()
{
int x=5;
int *p;
p=&x;
printf("Value of x :%d",*p);
return 0;
}

// program to increment the value of a variable using pointer
#include<stdio.h>
int main()
{
int x=4;
int *p;
p=&x;
printf("Value of X before incrementing:%d\n",x);
*p=*p+1;
printf("Value of X after incrementing:%d",x);
return 0;
}

// Accessing value of a variable using Pointer to pointer
#include<stdio.h>
int main()
{
int a=10;
int *p,**q;
p=&a;
q=&p;
printf("Value of a :%d",**q);
return 0;
}

// program for knowing size of pointer,and also size of the data type that it is pointing to
#include<stdio.h>
int main()
{
int *p;
float *q;
double *r;
char *ch;
//size of the pointers
printf("Size of pointer p: %lu\n",sizeof(p));
printf("Size of pointer q: %lu\n",sizeof(q));
printf("Size of pointer r: %lu\n",sizeof(r));
printf("Size of pointer ch: %lu\n",sizeof(ch));
//sizes of data types that pointers are pointing
printf("Size of int: %lu\n",sizeof(*p));
printf("Size of float: %lu\n",sizeof(*q));
printf("Size of double: %lu\n",sizeof(*r));
printf("Size of char: %lu\n",sizeof(*ch));
return 0;
}

// program to swap two numbers using pointers
#include<stdio.h>
void swap(int *,int *);
int main()
{
int a=5,b=10;
printf("Values of a and b before swapping:\n");
printf("a=%d , b=%d\n",a,b);
swap(&a,&b);
printf("Values of a and b after swapping:\n");
printf("a=%d , b=%d\n",a,b);
return 0;
}
void swap(int *a,int *b){
int temp;
temp=*a;
*a=*b;
*b=temp;
}

// Program to print sum of three numbers and also find maximum of three
void sumAndMax(int ,int ,int ,int*,int*);
#include<stdio.h>
int main()
{
int a=50,b=90,c=20,sum,max;
sumAndMax(a,b,c,&sum,&max);
printf("Sum= %d , Maximum number= %d",sum,max);
return 0;
}
void sumAndMax(int x,int y,int z,int *p,int *q){
*p=x+y+z;
*q=(x>y && x>z)?x:(y>z?y:z); // greatest of three numbers using ternary operator
}

// Program to print array elements using pointers
#include<stdio.h>
void printArray(int*,int);
int main()
{
int a[]={10,20,30,40,50};
printArray(a,sizeof(a)/sizeof(a[0]));
return 0;
}
void printArray(int *ptr_arr,int size){
int i;
for(i=0;i<size;i++)
{
printf("%4d",*(ptr_arr+i));
}
}

// program to read a string from the user and convert characters in lower case to upper
// and the characters which are in uppercase to lower uaing pointers.
#include<stdio.h>
void toggleChar(char*);
int main()
{
char str[50];
printf("Enter the string:");
scanf("%[^\n]",str);
toggleChar(str);
printf("Converted string is: %s",str);
return 0;
}
void toggleChar(char *ptr_ch){
int i;
for(i=0;*(ptr_ch+i)!='\0';i++){
if(*(ptr_ch+i)>='A' && *(ptr_ch+i)<='Z'){
*(ptr_ch+i)=*(ptr_ch+i)+32;
}
else if(*(ptr_ch+i)>='a' && *(ptr_ch+i)<='z'){
*(ptr_ch+i)=*(ptr_ch+i)-32;
}
}
}

// program to store data dynamically using malloc and print it
#include<stdio.h>
#include<stdlib.h>

int main()
{
int *p,n,i;
printf("Enter number of elements to be stored:");
scanf("%d",&n);
p=(int*)malloc(n*sizeof(int));
if(p==NULL){
printf("Cannot allocate memory");
exit(1);
}
printf("Enter %d elements:",n);
for(i=0;i<n;i++)
{
scanf("%d",p+i);
}
printf("The entered elements are:");
for(i=0;i<n;i++){
printf("%4d",*(p+i));
}
free(p);
return 0;
}

// program to store data dynamically using calloc and print it
#include<stdio.h>
#include<stdlib.h>

int main()
{
int *p,n,i;
printf("Enter number of elements to be stored:");
scanf("%d",&n);
p=(int*)calloc(n,sizeof(int));
if(p==NULL){
printf("Cannot allocate memory");
exit(1);
}
printf("Enter %d elements:",n);
for(i=0;i<n;i++)
{
scanf("%d",p+i);
}
printf("The entered elements are:");
for(i=0;i<n;i++){
printf("%4d",*(p+i));
}
free(p);
return 0;
}

// program to store data dynamically using calloc and extend the existing data using realloc and print it
#include<stdio.h>
#include<stdlib.h>

int main()
{
int *p,n,i,k;
printf("Enter number of elements to be stored:");
scanf("%d",&n);
p=(int*)calloc(n,sizeof(int));
if(p==NULL){
printf("Cannot allocate memory");
exit(1);
}
printf("Enter %d elements:",n);
for(i=0;i<n;i++)
{
scanf("%d",p+i);
}
printf("The entered elements are:");
for(i=0;i<n;i++){
printf("%4d",*(p+i));
}
printf("\nEnter number of elements you want to extend:");
scanf("%d",&k);
p=(int*)realloc(p,k*sizeof(int));
if(p==NULL){
printf("Cannot allocate memory");
exit(1);
}
printf("Enter the next %d elements:",k);
for(i=0;i<k;i++)
{
scanf("%d",(p+n+i));
}
printf("The entered elements after extending are:");
for(i=0;i<n+k;i++){
printf("%4d",*(p+i));
}
free(p);
return 0;
}

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