#include<stdio.h>
int main(){
  int a,b,c,big;
  printf("\nEnter 3 numbers:");
  scanf("%d %d %d",&a,&b,&c);

  big=(a>b&&a>c?a:b>c?b:c);
  printf("\nThe biggest number is: %d",big);

  return 0;
}

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

long int num,sum,r;
printf("\nEnter a number:-");
scanf("%ld",&num);

while(num>10){
sum=0;
while(num){
r=num%10;
num=num/10;
sum+=r;
}
if(sum>10)
num=sum;
else
break;
}
printf("\nSum of the digits in single digit is: %ld",sum);
return 0;
}

#include <stdio.h>
int main(){         
int num,x;
printf("Enter any number: ");
scanf("%d",&num);
printf("Generic root: %d",(x=num%9)?x:9);
return 0;
}
Sample output:
Enter any number: 731
Generic root: 2

#include<stdio.h>
int main(){
  int num,i=1,j,k;
  printf("\nEnter a number:");
  scanf("%d",&num);
  while(i<=num){
      k=0;
      if(num%i==0){
         j=1;
          while(j<=i){
            if(i%j==0)
                 k++;
             j++;
          }
          if(k==2)
             printf("\n%d is a prime factor",i);
      }
      i++;
   }
   return 0;
}

#include<stdio.h>
int main(){
  int n,r,ncr;
  printf("Enter any two numbers->");
  scanf("%d %d",&n,&r);
  ncr=fact(n)/(fact(r)*fact(n-r));
  printf("The NCR factor of %d and %d is %d",n,r,ncr);
  return 0;
}
 int fact(int n){
  int i=1;
  while(n!=0){
      i=i*n;
      n--;
  }
  return i;
 }