Thread: generate non repeat numbers

hi, i need generate 5 diferent nubmers from 1 to 10, without repeating.

Code:

#include<stdio.h>
#include <stdlib.h>
#include <time.h>

#define N 5
void main()
{
 int i,j,index;
 int mas[N];
 int random_integer;

srand ( time(NULL) );
for(index=0; index<5; index++){
random_integer = (rand()%10)+1;

mas[i]=random_integer;
  j=0;
  for ( i = 0; i< 5; i++ ) {
    if ( mas[j] == random_integer );
      break;
  }

  if ( j == i )
		mas[i] = random_integer;
		printf("%5d", mas[i]);
}
     }

i can`t understand how i should compare array elements, so in the output wouldnt be two indetical elements. Thank you

Actually, I'd start with simply loading a 10 element array up with the numbers 1 through 10, and then just shuffling them, and picking off the first five.

For 10 numbers, just brute-force generating randoms and testing for uniqueness is probably fine, but if you ever tried the same thing with a larger working set, you could be in a world of processor bound hurt.

thanks , but i just want to understand and fix my error with my generator

i modified your code little bit this is also the one way which i thought

Code:

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

#define MAX_NUMBER 10

void main() {
  int index                    = 0;
  int number_table[MAX_NUMBER] = {0};
  int random_integer           = 0;
  int number_count             = 0;

  srand ( time(NULL) );

  while (number_count < 5) {
    random_integer = (rand() % 10) + 1;
    if (number_table[random_integer - 1] == 0) {
      number_table[random_integer - 1] = 1;
      ++number_count;
    }
  }

  index = 0;
  for (; index < MAX_NUMBER; ++index)
    if (number_table[index] == 1)
      printf("%d  ", index + 1);

  return 0;
}

Rocky, that code will NOT generate a randomized 5 number selection. It will always be an 'In Order' selection, which removes quite a bit of the randomness.

Did u acually looked at the code there or you are just doing posing to increment the post count

printing of random numbers will be in sequence and the genration will be in random order if you want that

if you want printing also you can put the printf in while loop


like the code below

Code:

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

#define MAX_NUMBER 10

void main() {
  int index                    = 0;
  int number_table[MAX_NUMBER] = {0};
  int random_integer           = 0;
  int number_count             = 0;

  srand ( time(NULL) );

  while (number_count < 5) {
    random_integer = (rand() % 10) + 1;
    if (number_table[random_integer - 1] == 0) {
      number_table[random_integer - 1] = 1;
      ++number_count;
      printf("%d  ", random_integer);
    }
  }
#if 0
  index = 0;
  for (; index < MAX_NUMBER; ++index)
    if (number_table[index] == 1)
      printf("%d  ", index + 1);
#endif
  return 0;
}

thanks Rocky, your code works great

no, the order doesnt matter. But like I said, rocky wrote the code, which works excellent, an now i can move forward with my main task. anyway, thanks for trying help

your actual code is also correct use mas[index]=random_integer instead of mas[i]=random_integer because you are using an uninitialized value of i .

thanks for all your advices . But i have one small problem. How to get all 5 values, after while? I can gen only last, maybe someone can help? for example, after while i have, if(random_integer=1) printf("done"), if (random_integer=2) printf("done2"), etc. If, generators, generates 1;2;3;4;5, i can use only 5, and i don`t know how to get all 5 values after while