C questions and answer with explanation

1. PERFECT NUMBER.

void main()

{

  int n,i=1,sum=0;

  clrscr();

  printf("\nEnter a number:-");

  scanf("%d",&n);

  while(i<n)

  {

            if(n%i==0)

            sum=sum+i;

            i++;

  }

    if(sum==n)

            printf("\nThe no %d is a perfect number",i);

    else

            printf("\nThe no %d is not a perfect number",i);

  getch();

}

2. ARMSTRONG NUMBER.

void main()

{

  int num,r,sum=0,temp;

  clrscr();

  printf("\nEnter a number:-");

  scanf("%d",&num);

  temp=num;

  while(num!=0)

  {

            r=num%10;

            num=num/10;

            sum=sum+(r*r*r);

  }

    if(sum==temp)

            printf("\nThe number %d is an armstrong number",temp);

    else

            printf("\nThe number %d is not an armstrong number",temp);

  getch();

3. STRONG NUMBER

void main()

{

  int num,i,f,r,sum=0,temp;

  clrscr();

  printf("\nEnter a number");

  scanf("%d",&num);

  temp=num;

  while(num)

  {

            i=1,f=1;

            r=num%10;

            while(i<=r)

            {

                        f=f*i;

                        i++;

            }

            sum=sum+f;

            num=num/10;

  }

   if(sum==temp)

            printf("%d is a strong number",temp);

   else

            printf("%d is not a strong number",temp);

  getch();

}

4. PRIME NUMBER.

void main()

{

  int num,i,count=0;

  clrscr();

  printf("\nEnter a number:");

  scanf("%d",&num);

  for(i=1;i<=num;i++)

  {

            if(num%i==0)

               count++;

  }

   if(count==2)

            printf("%d is a prime number",num);

   else

            printf("%d is not a prime number",num);

  getch();

}

5. REVERSE A NUMBER

void main()

{

  int num,sum=0,r;

  clrscr();

  printf("\nEnter a number:");

  scanf("%d",&num);

  while(num)

  {

            r=num%10;

            sum=sum*10+r;

            num=num/10;

  }

   printf("\nReverse number=%d",sum);

  getch();

}

6. SUM OF THE DIGITS OF A NUMBER

void main()

{

  int num,sum=0,r;

  clrscr();

  printf("\nEnter a number:");

  scanf("%d",&num);

  while(num)

  {

            r=num%10;

            num=num/10;

            sum=sum+r;

  }

   printf("sum=%d",sum);

  getch();

}

7. PALINDROME NUMBER.

void main()

{

  int num,r,sum=0,temp;

  clrscr();

  printf("\nEnter a number:");

  scanf("%d",&num);

  temp=num;

  while(num)

  {

            r=num%10;

            num=num/10;

            sum=sum*10+r;

  }

   if(temp==sum)

            printf("\n%d is a palindrome",temp);

   else

            printf("\n%d is not a palindrome",temp);

  getch();

}

8. G.C.D OF TWO NUMBERS

void main()

{

  int n1,n2;

  clrscr();

  printf("\nEnter two numbers:");

  scanf("%d %d",&n1,&n2);

  while(n1!=n2)

  {

            if(n1>n2)

                        n1=n1-n2;

            else

                        n2=n2-n1;

  }

   printf("\nGCD=%d",n1);

  getch();

}

9. L.C.M OF TWO NUMBERS.

void main()

{

  int n1,n2,x,y;

  clrscr();

  printf("\nEnter two numbers:");

  scanf("%d %d",&n1,&n2);

  x=n1,y=n2;

  while(n1!=n2)

  {

            if(n1>n2)

                        n1=n1-n2;

            else

                        n2=n2-n1;

  }

   printf("L.C.M=%d",x*y/n1);

  getch();

}

10. SWAP TWO VARIABLES WITHOUT USING THIRD VARIABLE

void main()

{

  int a,b;

  clrscr();

  printf("\nEnter two numbers:");

  scanf("%d %d",&a,&b);

  printf("\nBefore swapping a=%d b=%d",a,b);

            a=a^b;

            b=b^a;

            a=a^b;

  printf("\nAfter swapping a=%d b=%d",a,b);

  getch();

}

11. FLOYD’S TRIANGLE

1

2 3

4 5 6

void main()

{

  int i,j,r,k=1;

  clrscr();

  printf("\nEnter the range:");

  scanf("%d",&r);

  printf("\nFLOYD'S TRIANGLE\n\n");

  for(i=1;i<=r;i++)

  {

            for(j=1;j<=i;j++,k++)

                        printf(" %d",k);

            printf("\n");

  }

  getch();

}

12. PRIME FACTORS OF A NUMBER

void main()

{

  int num,i=1,j,k;

  clrscr();

  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++;

  }

  getch();

}

13. MULTIPLICATION TABLE

void main()

{

  int r,i,j,k;

  clrscr();

  printf("\nEnter the number range:-");

  scanf("%d",&r);

  for(i=1;i<=r;i++)

  {

            for(j=1;j<=10;j++)

                     printf(" %d*%d=%d",i,j,i*j);

            printf("\n");

  }

  getch();

}

14. FACTORIAL OF A NUMBER

void main()

{

  int i=1,f=1,num;

  clrscr();

  printf("\nEnter a number:");

  scanf("%d",&num);

  while(i<=num)

  {

            f=f*i;

            i++;

  }

  printf("\nFactorial of %d is:%d",num,f);

  getch();

}

15. FIBONACCI SERIES

void main()

{

  int i=0,j=1,k=2,r,f;

  clrscr();

  printf("Enter the number range:");

  scanf("%d",&r);

  printf("\nFIBONACCI SERIES: ");

  printf("%d %d",i,j);

  while(k<r)

  {

            f=i+j;

            i=j;

            j=f;

            printf(" %d",j);

            k++;

  }

  getch();

}