CODEWITHSUNDEEP
csrand
Harsh Jani
Harsh Jani

Reputation: 13

Simple C Program Error..Can't resolve it

I'm trying to generate random numbers in C using srand(). I want to generate numbers from 1 to 25 without duplication, So i have implemented the following program.

#include <stdio.h> 
#include <time.h>
int main()
{
int i=0,n,a[25]={0},b[25]={0},cntr=0;
srand(time(NULL));
while(cntr!=25)
{
    n=rand()%26;
    if(n!=9)
    {
        if(a[n]!=1)
        {
            a[n]=1;
            printf("%d  ",n);
            b[i]=n;
            printf("%d\n",b[i]);
            cntr++;
            i++;
        }
    }
}
for(i=0;i<25;i++)
{
    printf("%d  ",b[i]);
}
return 0;
}

Now there is a weird problem. When i print the array b inside the loop where the random number is generated it prints correct numbers. But when i print it outside the loop the first element of the array b changes to 1 and i get duplicate value of 1 in the random numbers. I would appreciate if anyone can help to find error in the program.

Here is the link to ideone where i have provided the output of the program : Ideone Link

Upvotes: 0

Views: 206

Answers (2)

user3629249
user3629249

Reputation: 16540

there are several little oops in the posted code.
the following corrects those oops

#include <stdio.h>
#include <stdlib.h> // srand(), rand()
#include <time.h>   // time()

int main()
{
    int i=0; // generated number counter
    int n;  // generated number
    int a[25]={0}; // tracks which numbers have been generated
    int b[25]={0}; // random array of numbers 1...25

    srand(time(NULL));

    while(i<25)  // correct loop termination
    {
        n=rand()%25+1; // yields 0...24 +1 gives 1...25

        if(a[n]!=1)
        { // then, number not previously generated
            a[n]=1;   // indicate number generated

            printf("%d  ",n); // echo number

            // save number in current location in array 'b'
            b[i]=n;
            printf("%d\n",b[i]);  // echo number again

            i++; // step offset into array 'b' (and loop counter)
        } // end if
    } // end while

    for(i=0;i<25;i++)
    {
        printf("%d  ",b[i]);
    } // end for

    return 0;
}  // end function: main

Upvotes: 1

Basile Starynkevitch
Basile Starynkevitch

Reputation: 1

You declare a[25] but you access any of 26 elements since n=rand()%26;, so declare instead

 int i=0,n,a[26]={0},b[26]={0},cntr=0;

BTW, compile with all warnings and debug info (e.g. gcc -Wall -Wextra -g). Then use the debugger (gdb). A watchpoint would have helped.

Upvotes: 2

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