Assiging Random Values to an Array in C

Question

    #include <conio.h>
#include <time.h>

int i = 1;



int main()
{
   int nums[20];

   srand(time(NULL));

   while(i < 20){
        nums[i] = rand()% 10;
        i++;

   }
    printf("%d\n%d\n%d\n%d\n%d\n%d\n%d\n%d\n%d\n%d\n%d\n%d\n%d\n%d\n%d\n%d\n%d\n%d\n%d\n%d\n", nums[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20]);
}

when I run this code I am given values I expect, Ie under 10, except for the values for 2, 3, and 4, and more often than not 4 is negative.... Any help on what I have done wrong would be appriciated

printf("%d\n%d\n%d\n%d\n%d\n%d\n%d\n%d\n%d\n%d\n%d\n%d\n%d\n%d\n%d\n%d\n%d\n%d\n%d\n%d\n", nums[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20]); could perhaps be written more clearly. In fact, I don't think the last argument makes any sense — Mateen Ulhaq
– Mateen Ulhaq, Commented Oct 11, 2016 at 1:43

AlexD · Accepted Answer · 2016-10-11 01:56:10Z

3

nums[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20]

is equivalent to

nums[20]

due to the funny ,-operator.

Try enumerating elements like this (starting with 0):

nums[0], nums[1], ..., num[19]

And initialize i to 0:

i = 0;

Or, although it is usually looks suspicious, start at 1, but then declare

int nums[21];

edited Oct 11, 2016 at 1:56

answered Oct 11, 2016 at 1:44

AlexD

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1 Comment

Jonathan Leffler Over a year ago

And make i into a local variable, not a global.

Mateen Ulhaq · Accepted Answer · 2016-10-11 01:45:40Z

2

Write your last line as a loop instead:

for(int i = 0; i < 20; i++)
    printf("%d\n", nums[i]);

answered Oct 11, 2016 at 1:45

Mateen Ulhaq

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2 Comments

Ed Goodman Over a year ago

That has got it to run as expected, do you know what it was I was doing incorrectly?

Mateen Ulhaq Over a year ago

As @AlexD said, you cannot index arrays like nums[1, 2, 3, ...] because (1, 2, 3, ...) evaluates to 20.

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