Thread: Question about code

hello,everyone,i just saw a program in c that computes all carmichael numbers to a MAXNUMB defined constant.The whole program up on computing the carmichael numbers is based on Korselt's criterion(see link above in wiki).Even though i understand the general philosophy of the algorithm i still have some questions about it..I want someone to explain me the red code actually if possible..It's where this temp confuses me a bit..It's maybe obvious or ridiculous to explain but at this time at night i thought i will give it a try and post it here.Thanks in advance!

Code:

#include <stdio.h>
#include <math.h>
#define MAXNUMB 1000000

main()
{ 
      int N,d,a,b,temp;
      
      for (N=561;N<=MAXNUMB;N+=2) {                        
          a=0;
          b=0;
          for (d=3;d<=sqrt(N);d+=2)                       
                        if  (N%(d*d)==0)                           
                             a=1;
          if (a==0){
                temp=N;
				for (d=3;d<=(temp);d+=2) {
				    if (temp%d==0){
                                 if ((N-1)%(d-1)!=0)              
                                                     a=1;
                                 else{
                                      temp/=d;
                                      b++;
                                 }
                    }
                }              
        }
		  if ((a==0)&&(b>1)){                                 
				temp=N;
				printf("%d is a Carmichael number: ", N);
			  for (d=3; d<=(temp);d+=2){
				  if (temp%d==0){
						printf("%d ", d);
						temp/=d;
						}
                  }
               printf("\n");
		  }
          }  
          printf("Done!");

The reason they use temp is because they actually want to do calculations using N, but they need to change that value in subsequent iterations of the for(d=3; ...) loops. They don't want to lose the value in N, so they use temp instead, and modify that. You can try reading the code as though temp were replaced by N everywhere.