#include<stdio.h>
int main(){
    int num,reverse;

    printf("Enter any number: ");
    scanf("%d",&num);

    reverse=rev(num);
    printf("Reverse of number: %d",reverse);
    return 0;
}

int rev(int num){
    static sum,r;

    if(num){
         r=num%10;
         sum=sum*10+r;
         rev(num/10);
    }
    else
         return 0;

    return sum;
}
Sample output:
Enter any number: 456
Reverse of number: 654

#include<stdio.h>
int main(){
  int num,sum=0,r;
  printf("Enter a number: ");
  scanf("%d",&num);
  while(num){
      r=num%10;
      num=num/10;
      sum=sum+r;
  }
  printf("Sum of digits of number:  %d",sum);
  return 0;
}
Sample output:
Enter a number: 123
Sum of digits of number:  6

#include<stdio.h>
int main(){
  int num,sum=0,r;
  printf("Enter a number: ");
  scanf("%d",&num);

  for(;num!=0;num=num/10){
      r=num%10;
      sum=sum+r;
  }
  printf("Sum of digits of number:  %d",sum);
  return 0;
}
Sample output:
Enter a number: 567
Sum of digits of number:  18

#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;
}