CODEWITHSUNDEEP
carrays
Noob programmer
Noob programmer

Reputation: 49

printing values in 2d 10x10 table, in C

Am trying to print out the values that are prime and not prime onto a 10x10 table. Arrays are confusing and cannot seem to get it, but I am assuming I need an array. The double XX on the expected output are just white space if the value is not prime.

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

int main()
{
    int i, j;


    for (i = 2; i <= 101; i++)
    {
        for (j = 2; j <= i; j++)
        {
            if ( i % j == 0)
            {   
                printf(" ");
                break;
            }
         }
         if( i == j)
         {
            printf("%d", i);
         }
    }
    return 0;
}

Expected output:

02 03 XX 05 XX 07 XX XX XX 11  
XX 13 XX XX XX 17 XX 19 XX XX  
XX 23 XX XX XX XX XX 29 XX 31  
XX XX XX XX XX 37 XX XX XX 41  
XX 43 XX XX XX 47 XX XX XX XX  
XX 53 XX XX XX XX XX 59 XX 61  
XX XX XX XX XX 67 XX XX XX 71
XX 73 XX XX XX XX XX 79 XX XX
XX 83 XX XX XX XX XX 89 XX XX
XX XX XX XX XX 97 XX XX XX 101

Upvotes: 0

Views: 4155

Answers (3)

chux
chux

Reputation: 153348

Divide and conquer: compute "is it a prime" and "print array" as separate problems.

The key is to break the task into manageable parts - architect the solution - and than implement the pieces. Use constants like I_MAX rather than use a naked magic number like 101. With the print_array(), think of how to print 1 element and wrap that into a loop of 10. Then wrap that loop into something that stops when all the numbers are printed.

#include <stdio.h>
#include <stdbool.h>
#include <stdlib.h>
#define I_MIN 2
#define I_MAX 101

// OP all ready has code for IsPrime() - here is an alternative
bool IsPrime(int i, const bool *set) {
  if (i <= 3) {
    return i >= 2;
  }
  int divisor = 2;
  for (;;) {
    if (i % divisor == 0) {
      return false;
    }
    if (i / divisor <= divisor) {
      return true;
    }
    // get next prime
    while (!set[++divisor])
      ;
  }
}

void print_array(const bool *set, int min, int max) {
  int width = 10;
  for (int i = min; i <= max;) {
    for (int w = 0; w < width; w++) {
      // Print the number
      if (set[i]) printf("%02d ", i);
      else fputs("XX ", stdout);
      i++;
      if (i > max)
        break;
    }
    fputc('\n', stdout);
  }
}

int main(void) {
  bool set[I_MAX + 1];  

  // Populate the set
  for (int i = 0; i <= I_MAX; i++) {
    set[i] = IsPrime(i, set);
  }

  // display the set
  print_array(set, I_MIN, I_MAX);
  return 0;
}

Upvotes: 2

thelaws
thelaws

Reputation: 8001

If it's just issues with formatting, it looks like you're missing the newline between rows. Before the end of your outer for loop add:

if((i -1) % 10 == 0) printf("\n");

This condition prints a newline every 10 iterations. The -1 is needed because the outer loop is started at 2.

Upvotes: 1

CinchBlue
CinchBlue

Reputation: 6190

What? No, no, no, you don't have to do all this complex stuff.

Just use a double loop: http://coliru.stacked-crooked.com/a/bc57bd52c29a419f

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

int main()
{
    int i, j;
    int my_array[10][10];

    //Fill the array
    for (i = 0; i < 10; ++i) {
        for (j = 0; j < 10; ++j) {
            my_array[i][j] = 10*i + j;
        }
    }

    //Print out the array
    for (i = 0; i < 10; ++i) {
        for (j = 0; j < 10; ++j) {
            printf("%d ", my_array[i][j]);
        }
        printf("\n");
    }


    return 0;
}

Make sure you get the indexing right. It should be relatively simple; never access the 10th index of an array of 10 elements; it's 0-9 and make sure that you print out the right value.

Upvotes: 3

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