C programming langauge: C program to print list of perfect numbers up to given range.

Because  6 is the smallest perfect number in number system, so we will find list of perfect numbers   from 6 to 10000.
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#include<stdio.h>
#include<conio.h>
void main()
{
int num,i,sum,n,cnt=0;
printf("\nEnter number:");
scanf("%d",&n);
     for(num=6;num<=n;num++)
     {
sum=0;
for(i=1;i<=num/2;i++)
{
if(num%i==0)
sum=sum+i;
}
if(sum==num)
printf("\n%d. PERFERCT NUMBER %d. ",++cnt,num);
if(cnt==4)
break;
}
getch();
}

C programming language: C program to check given number is perfect number or not.

Perfect number is a positive integer number  that is equal to the sum of its divisors.
Example: 6 is the smallest perfect number in number system.
                Here divisors of 6 is 1,2 and 3.
                Here 1+2+3=6 is a perfect number.
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#include<stdio.h>
#include<conio.h>
void main()
{
int num,i,sum=0;
printf("\nEnter Number To Check :");
scanf("%d",&num);
     for(i=1;i<=num/2;i++)
     {
       if(num%i==0)
  sum=sum+i;
     }
   if(num==sum)
     printf("\n %d Is a Perfect Number...",num);
else
printf("\n %d Is Not a Perfect Number...",num);
getch();
}

C programming language: Prime number program in c.

// simple code but not optimized much.
#include<stdio.h>
#include<conio.h>
void main()
{
int i,n,flag=0;
printf("\nEnter Number to Check Prime: ");
scanf("%d",&n);
for(i=2;i<n/2;i++)
{
if(n%i==0)
{
flag=1;
        break;
}

else
flag=0;
}
if(flag==0)
printf("\nGiven Number is prime:");
else
    printf("\nGiven Number is Not prime: ");
getch();
}




// simple and optimized code. 

#include<stdio.h>

#include<conio.h>
void main()
{
int p=2;
int n,num;
printf("\nEnter Number to Check Prime: ");
scanf("%d",&num);
n=num;
while(num%p++!=0);  // dummy while loop 
if(p>num)
printf("\nGiven Number is prime:");
else
printf("\nGiven Number is Not prime:");
getch();
}

C programming language: C program to calculate/ find sum of super digits using recursion.

For Example:- 
                 super digit of 9875 will be calculated as:

super-digit(9875) = super-digit(9+8+7+5) 
                  = super-digit(29) 
                  = super-digit(2+9)
                  = super-digit(11)
                  = super-digit(1+1)
                  = super-digit(2)
                  = 2.

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#include<stdio.h>
#include<conio.h>
int recSum(int n);
void main()
{
int n,ans;
printf("\n Enter number: ");
scanf("\n%d",&n);
ans=recSum(n);
printf("\n Sum:=%d",ans);
getch();
}

int recSum(int n1)
{
int rem,sum=0;
if(n1==0)
return 0;
else
{
rem=n1%10;
sum=rem+recSum(n1/10);
}

if(sum>9)
{
n1=sum;
sum=recSum(n1);
}
return sum;
}

C programming language: C program for sum of digits.

#include<stdio.h>
#include<conio.h>
void main()
{
int n,sum=0;
int rem;
printf("\nEnter Number: ");
scanf("%d",&n);
 while(n)
  {
   rem=n%10;
   sum=sum+rem;
   n=n/10;
   }
              printf("Sum of Digits: %d",sum);
      getch();
}