Q:

C Program: Updating max and min integers without using arrays

I'm experimenting with a simple C program that should prompt user to enter a chosen number of positive integers. I'm having an issue getting the maximum and minimum of the set of integers I input without the use of an array. 
The way that I currently have it is that it will update the max and min among the last two entered values. If someone wouldn't mind looking to see what I'm doing wrong, it would be appreciated. 
take a look here:
#include<stdio.h>

int main()
{
   int N ,i, value=0, min=0, max=0, sum=0, oldmin=0, Newmin=0, oldmax=0, Newmax=0;
double mean;

do{

  printf("How many values are to be entered?: ");
  scanf("%d", &N);
  printf("\n");

  if (N>0){

  do{   
     if (N>0){

                                // 1st value updated
     for (i=1;i<=N;i++)
     {   

         printf("Value %d:\n",i);
         scanf("%d", &value);
         sum  = sum+value; 
      }
       mean = (double)sum/(double)N;

      //max
         if(oldmax<Newmax){
            max = Newmax;
         }
         else max = oldmax;

      //min
        if(oldmin>Newmin){
            min = Newmin;
         }
         else min = oldmin;

  }

  else printf("INPUT ERROR!\n");
  }
  while(N<0);
      printf("\nThe minimum value is %d, the maximum value is %d, and the average value is %.2lf.",min,max,mean);

      }else printf("INPUT ERROR!\n");
  } while(N<0);

return 0;}

A:

if(oldmax<Newmax){

Don't compare newmax and oldmax. Compare max and value. Same with min.
I'm not even sure about the purpose of Newmax and oldmax. Remove these variables all-together, as it will just confuse you.
Just use min, max, and value. It will sort out.

A:

some remarks :

you need to set the min/max value from value in the same loop you do sum  = sum+value; , this is the reason of your problem about min/max
check the scanf result to be sure a number was enter
if (N>0){ do{ if (N>0){ so two check but N never change
if (N > 0)  { do { ... } while (N<0); } that has no sense
the embedded loops have no sense, only 1 loop is needed 

A proposal removing the problems :
#include<stdio.h>

int main()
{
   int N;

   fprintf(stderr, "How many values are to be entered?: ");
   if ((scanf("%d", &N)  != 1) || (N <= 0))
     printf("INPUT ERROR!\n");
   else {
     int i, min, max, sum = 0;

     for (i = 0; i < N; ++i) {
       int value;

       fprintf(stderr, "Value %d:\n",i);
       if (scanf("%d", &value) != 1) {
         printf("INPUT ERROR!\n");
         return -1;
       }
       sum  = sum+value; 
       if (i == 0) {
         min = max = value;
       }
       else {
         if (value < min)
           min = value;
         if (value > max)
           max = value;
       }
     }

     printf("\nThe minimum value is %d, the maximum value is %d, and the average value is %.2lf\n",
            min,max, (double)sum/(double)N);
   }

   return 0;
}

Compilation and execution :
pi@raspberrypi:/tmp $ gcc -g -pedantic -Wextra c.c
pi@raspberrypi:/tmp $ ./a.out
How many values are to be entered?: 3
Value 0:
1
Value 1:
2
Value 2:
3

The minimum value is 1, the maximum value is 3, and the average value is 2.00

I used fprintf to flush the message with a \n, and I set the first min and max value on the first turn to not have to use the MIN_INT MAX_INT may be not defined for you

