random number generator array

hey i having problems with solving this question:
Write a program that generates an array of 20 random numbers between 1 and 100. Use a loop to
output the numbers on the screen with a field width of 4 characters. Write code that will reverse the
numbers in the array and then output the numbers to the screen with a copy of the same output loop
used with the original numbers.

Please help :)

What kind of errors are you getting?

Quote:

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array of 20

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Code:

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int arr [20] ;

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Quote:

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20 random numbers

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rand () and srand ()

Quote:

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Use a loop

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Code:

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int i ;
for (i = 0; i < 20; ++i) {
...
}

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Quote:

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output the numbers on the screen with a field width of 4 characters

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printf () formatting

Quote:

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reverse the numbers

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A swap () function

Or copy them backwards into a second array.

Quote:

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Please help

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Homework help

i have filled the array with random numbers and got it to print with a feild width of 4 characters i just dont know figure out how to print the array data in reverse. this is what i have:

Code:

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int main()
{
          int array[20], i;
          for(i = 0; i < 20; i++)
          {
                  array[i] = (rand() % 100)+1;
                  printf("%4d\n", array[i]);
      }
    return 0;
}

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Write a second loop that starts from the last element to print them.

Quote:

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Originally Posted by laserlight

Write a second loop that starts from the last element to print them.

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hey laserlight
so say the first 3 integers in the array are:
45
100
20
how would i switch all numbers in the array to:
54
001
02
(opposite)?
thankyou for your help :)

It's easy enough to print numbers in reverse.

Just go

Code:

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for(i=N-1;i>=0;i--)
  printf("%d\n", array[i]);

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But you're not allowed to do this. You have to reverse the array. So you have to step throuhg half of it, swapping very ith element with the N-i-1th element. It's a bit tricky to get all the cases right.

To generate random number on 0 to N-1, the cheap and nasty way is rand() % N. This doesn't give a very good distribution, because rand() isn't truly random and the lower bits are less random than the whole.
So the best way to to say

Code:

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/* random number on 0-1 minus a tiny epsilon */
#define uniform() (rand()/RAND_MAX+1.0))

/* random number on 0-N */
#define rnd(N) (int) (uniform() * (N))

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Quote:

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Originally Posted by werty2480

so say the first 3 integers in the array are:
45
100
20
how would i switch all numbers in the array to:
54
001
02
(opposite)?

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If you need to reverse the order of the digits in a number you could use a combination of modulo (%) and divisior.

Bye, Andreas