Thread: 2d arrray,pick among a number of values to print randomly

hi,
i want to print Largest number from any 5 rows.Th number printed should be any one of the largest in the five rows of 2d arrays.I have created code for largest number in each row but how to pick and print them randomly?.

Code:

 #include<conio.h>
 
main( )
{ 
  int a,b,c,d,e,x;
  int arr[] = {a,b,c,d,e};
  int Matrix[5][5] ={            /*Initializing array*/                
                      2,4,3,5,9,
                      6,8,2,2,10,
                      9,12,345,23,5,
                      45,67,349,234,56,
                      23,34,64,347,6
                    };    
                    
                     
 printf ( "Largest number from any 5 rows is : ") ;
 a= ROW(&Matrix[0][0]);
 b= ROW(&Matrix[1][0]);
 c= ROW(&Matrix[2][0]);
 d= ROW(&Matrix[3][0]);
 e= ROW(&Matrix[4][0]);
 
 x = ;/*<===here i want any value of the array arr[]*/
 printf("\n%d",x);
 }
 
 ROW(int *a)
 {
  int i,j,temp;
  temp = *a;
  for(j=1;j<=4;j++)
   {
    if (temp<*(a+j))
    temp = *(a+j);
   }
  return(temp);
}

so why not to scan the whole array? Why only one row?
If you got 100x100 matrix you would use 100 variables for each line?

I interpret his question as asking for the largest element in a random row.

Originally Posted by Crossfire

simplist idea, get a random number between 1 and 4, then that would be your row number??? then send it to your "largest number in the row" function!!!

in other words..."how to pick...them randomly"



i would say learn how to seed then pick a random number! MANY MANY posts on here about that!



//edit//

oh pick one at random from entire array...

two random number picks...

array[random number 1][random number 2] ?

Tried that but the answer is always coming 345 (i.e ran() is only giving 2 as a value each time i run it).what is the problem here,why its not working properly?

Code:

 #include<stdio.h>
 
main( )
{ 
  int a;
  int Matrix[5][5] ={            /*Initializing array*/                
                      2,4,3,5,9,
                      6,8,2,2,10,
                      9,12,345,23,5,
                      45,67,349,234,56,
                      23,34,64,347,6
                    };    
                    
 
 printf ( "Largest number from any 5 rows is : ") ;
 a= ROW(&Matrix[rand()%4+1][0]);
 
 printf("\n%d",a);
 }
 
 ROW(int *a)
 {
  int i,j,temp;
  temp = *a;
  for(j=1;j<=4;j++)
   {
    if (temp<*(a+j))
    temp = *(a+j);
   }
  return(temp);
}

you need to use srand

Code:

#include <stdio.h> /* conio.h is not standard */
#include <stdlib.h> /* you need this for rand */
#include <time.h>

#define LINE_SIZE 5

int ROW(int *a); /* we need to have prototype before the function call */

int main(void)/* read FAQ */
{
    int a;
    //int arr[] = {a,b,c,d,e}; /* you are initializing array with not initialized variables - pointless */
    int Matrix[LINE_SIZE][LINE_SIZE] ={            /*Initializing array*/
        2,4,3,5,9,
        6,8,2,2,10,
        9,12,345,23,5,
        45,67,349,234,56,
        23,34,64,347,6
    }; 

    srand((unsigned int) time(NULL)); /* so that rand sequence be different for each run */
    
    a= ROW(&Matrix[rand()%LINE_SIZE][0]); /* why to skip first row ? */

    printf ( "Largest number from any 5 rows is : %d\n",a);

    return 0;
}

int ROW(int *a)
{
    int j,temp;
    temp = a[0];
    for(j=1;j<LINE_SIZE;j++)
    {
        if (temp<a[j])
            temp = a[j];
    }
    return temp;
}

Originally Posted by vart

you need to use srand

Code:

#include <stdio.h> /* conio.h is not standard */
#include <stdlib.h> /* you need this for rand */
#include <time.h>

#define LINE_SIZE 5

int ROW(int *a); /* we need to have prototype before the function call */

int main(void)/* read FAQ */
{
    int a;
    //int arr[] = {a,b,c,d,e}; /* you are initializing array with not initialized variables - pointless */
    int Matrix[LINE_SIZE][LINE_SIZE] ={            /*Initializing array*/
        2,4,3,5,9,
        6,8,2,2,10,
        9,12,345,23,5,
        45,67,349,234,56,
        23,34,64,347,6
    }; 

    srand((unsigned int) time(NULL)); /* so that rand sequence be different for each run */
    
    a= ROW(&Matrix[rand()%LINE_SIZE][0]); /* why to skip first row ? */

    printf ( "Largest number from any 5 rows is : %d\n",a);

    return 0;
}

int ROW(int *a)
{
    int j,temp;
    temp = a[0];
    for(j=1;j<LINE_SIZE;j++)
    {
        if (temp<a[j])
            temp = a[j];
    }
    return temp;
}

Thank you, that explains a lot and my program is working now.

I have one question does that mean rand() will not generate different numbers randomly until srand() is used ?

srand will 'seed' the random number generator, often using the system time, to create a different series of numbers - without that rand will give you a random series, but if you are repeatedly using it, it will always be the same.

You do not have to call srand repeatedly though, once will suffice.

Here is another thread that asks the same question

rand is pseudo-random generator which for the given seed value will produce same "random" sequence of values.

It is very convenient for testing of programs using rand() - when you encounter a bug with specific seed value - you just use same seed value each time you try to reproduce the bug till you fix it.