Question:Sum of digits in c using recursion 

#include<stdio.h>
int main(){
  int num,x;
  clrscr();
  printf("\nEnter a number: ");
  scanf("%d",&num);
  x=findsum(num);
  printf("Sum of the digits of %d is: %d",num,x);
  return 0;
}

int r,s;
int findsum(int n){
if(n){
         r=n%10;
         s=s+r;
         findsum(n/10);
     }
     else
       return s;
}

Question:Find power of a number using recursion using c program 

#include<stdio.h>
int main(){
  int pow,num;
  long int res;
  long int power(int,int);
  printf("\nEnter a number: ");
  scanf("%d",&num);
  printf("\nEnter power: ");
  scanf("%d",&pow);
  res=power(num,pow);
  printf("\n%d to the power %d is: %ld",num,pow,res);
  return 0;
}
  int i=1;
  long int sum=1;
  long int power(int num,int pow){
      if(i<=pow){
           sum=sum*num;
          power(num,pow-1);
      }
      else
      return sum;
  }

Question:How to find size of integer data type without using sizeof operator in c programming language 

#include<stdio.h>
int main(){
  int *ptr = 0;
  ptr++;
  printf("Size of int data type:  %d",ptr);
  return 0;
}

Question:How to find size of double data type without using sizeof operator in c programming language 

#include<stdio.h>
int main(){
  double *ptr = 0;
  ptr++;
  printf("Size of double data type:  %d",ptr);
  return 0;
}

Question:How to find size of structure data type without using sizeof operator in c programming language 

#include<stdio.h>
struct student{
    int roll;
    char name[100];
    float marks;
};

int main(){
  struct student *ptr = 0;
  ptr++;
  printf("Size of the structure student:  %d",ptr);
  return 0;
}

Question:How to find size of union data type without using sizeof operator in c programming language 

#include<stdio.h>
union student{
    int roll;
    char name[100];
    float marks;
};

int main(){
  union student *ptr = 0;
  ptr++;
  printf("Size of the union student:  %d",ptr);
  return 0;
}

Question:Concatenation of two strings using pointer in c programming language 

#include<stdio.h>
int main(){
  int i=0,j=0;
  char *str1,*str2,*str3;
  puts("Enter first string");
  gets(str1);
  puts("Enter second string");
  gets(str2);
  printf("Before concatenation the strings are\n");
  puts(str1);
  puts(str2);
  while(*str1){
      str3[i++]=*str1++;
  }
  while(*str2){
      str3[i++]=*str2++;
  }
  str3[i]='\0';
  printf("After concatenation the strings are\n");
  puts(str3);
  return 0;
}

Question:Write a simple code for linear search in c programming language 

#include<stdio.h>
int main(){

    int a[10],i,n,m,c=0;

    printf("Enter the size of an array: ");
    scanf("%d",&n);

    printf("Enter the elements of the array: ");
    for(i=0;i<=n-1;i++){
         scanf("%d",&a[i]);
    }

    printf("Enter the number to be search: ");
    scanf("%d",&m);
    for(i=0;i<=n-1;i++){
         if(a[i]==m){
             c=1;
             break;
         }
    }
    if(c==0)
         printf("The number is not in the list");
    else
         printf("The number is found");

    return 0;
}
Sample output:
Enter the size of an array: 5
Enter the elements of the array: 4 6 8 0 3
Enter the number to be search: 0
The number is found

Question:Write a simple code for binary search in c programming language 

#include<stdio.h>
int main(){

    int a[10],i,n,m,c=0,l,u,mid;

    printf("Enter the size of an array: ");
    scanf("%d",&n);

    printf("Enter the elements in ascending order: ");
    for(i=0;i<n;i++){
         scanf("%d",&a[i]);
    }

    printf("Enter the number to be search: ");
    scanf("%d",&m);

    l=0,u=n-1;
    while(l<=u){
         mid=(l+u)/2;
         if(m==a[mid]){
             c=1;
             break;
         }
         else if(m<a[mid]){
             u=mid-1;
         }
         else
             l=mid+1;
    }
    if(c==0)
         printf("The number is not found.");
    else
         printf("The number is found.");

    return 0;
}
Sample output:
Enter the size of an array: 5
Enter the elements in ascending order: 4 7 8 11 21
Enter the number to be search: 11
The number is found.

Question:Write a simple code for binary search using function recursion in c programming language 

#include<stdio.h>
int main(){

    int a[10],i,n,m,c,l,u;

    printf("Enter the size of an array: ");
    scanf("%d",&n);

    printf("Enter the elements of the array: " );
    for(i=0;i<n;i++){
         scanf("%d",&a[i]);
    }

    printf("Enter the number to be search: ");
    scanf("%d",&m);

    l=0,u=n-1;
    c=binary(a,n,m,l,u);
    if(c==0)
         printf("Number is not found.");
    else
         printf("Number is found.");

    return 0;
 }

int binary(int a[],int n,int m,int l,int u){

     int mid,c=0;

     if(l<=u){
          mid=(l+u)/2;
          if(m==a[mid]){
              c=1;
          }
          else if(m<a[mid]){
              return binary(a,n,m,l,mid-1);
          }
          else
              return binary(a,n,m,mid+1,u);
     }
     else
       return c;
}
Sample output:
Enter the size of an array: 5
Enter the elements of the array: 8 9 10 11 12
Enter the number to be search: 8
Number is found.