#include<stdio.h>

int getSum(int);
int main(){
  int num,sum;
  printf("Enter a number: ");
  scanf("%d",&num);

  sum = getSum(num);

  printf("Sum of digits of number:  %d",sum);
  return 0;
}

int getSum(int num){

    static int sum =0,r;

    if(num!=0){
      r=num%10;
      sum=sum+r;
      getSum(num/10);
    }

    return sum;
}
Sample output:
Enter a number: 45
Sum of digits of number:  9

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

#include<stdio.h>

int main(){
   
    int a,b;
    int sum;

    printf("Enter any two integers: ");
    scanf("%d%d",&a,&b);

    //sum = a - (-b);
    sum = a - ~b -1;

    printf("Sum of two integers: %d",sum);

    return 0;
}
Sample output:
Enter any two integers: 5 10
Sum of two integers: 15

#include<stdio.h>

int main(){
   
    int a,b;
    int sum;

    printf("Enter any two integers: ");
    scanf("%d%d",&a,&b);

    sum = a + ~b + 1;

    printf("Difference of two integers: %d",sum);

    return 0;
}
Sample Output:
Enter any two integers: 5 4
Difference of two integers: 1

#include<stdio.h>
int main(){
    int a,b,c;
    printf("\nEnter 3 numbers: ");
    scanf("%d %d %d",&a,&b,&c);
    if(a-b>0 && a-c>0)
         printf("\nGreatest is a :%d",a);
    else
         if(b-c>0)
             printf("\nGreatest is b :%d",b);
         else
             printf("\nGreatest is c :%d",c);
    return 0;
}