Need to be pointed in right direction

[nizbit]

This what I'm suppoesed to be doing. Allocate enough memory to hold 50 integers using malloc and assign the pointer returned by malloc to "ia". Using only "ip" populate the array with fifty random integers. Using only "ip" display the contents of the array both forward and backard. The function randnum was given. I'm not getting 50 random integers. Could someone tell me the problem area(s) where I should be looking at?

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

int randnum(int range);

int main () {

    int    *ia, *ip;
    
    srand(time(NULL));
    ia = malloc (50 * sizeof(int));
        
    if (ia == NULL) {
         
         printf("Cannot malloc\n");
         exit(1);
    }
        
    for (ip = ia; ip < ia + 50; ip++)
           *ip=randnum(50);
           printf("%-3d", *ip);

    return 0;
}

int randnum(int range) {

    int    v;
    v = rand();
    return (v * range / (RAND_MAX + 1));

}

[quzah]

If you're trying to have a range of zero to fifty or something (the 'range' parameter), why are you doing it the hard way?

int randnum( int range )
{
    return rand() % range;
}

Oh, the problem though is that you are only printing one number. You're not printing every time through the loop. Try surrounding those two lines with a pare of braces.

Quzah.

[Thantos]

Well using division by RAND_MAX does produce better result than mod. But of course this requires that you actually do the division correctly.

int randnum(int range) {

    int    v;
    v = rand();
    return (v * range / (RAND_MAX + 1));

}

Lets look at this
v = int
range = int
RAND_MAX = int
1 = int

So you are only doing integer division.
Now there are some other major problems

v * range can easily overflow the range an int can hold,
RAND_MAX + 1 could very likely overflow an int

Prelude has posted a very nice C++ random function that I won't try to reproduce here. Go search for it.

[Kleid-0]

You can find Prelude's article post about random functions here:
http://faq.cprogramming.com/cgi-bin/...&id=1043284385

[Thantos]

Thats not what I was refering to. Actually I realized after I posted this is the C forum and she posted it on the C++ forum using C++.

[Kleid-0]

I was having trouble searching for Prelude's post in the C forum, lol

[nizbit]

I have just one more question. I need to print the array forward and backwards. I think I have it down, but I want to add a couple of newlines between printing the whole array forwards and then backwards. I don't want columns.

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

int randnum(int range);

void main (void) {

    int    *ia, *ip;
    
    srand(time(NULL));
    ia = malloc (50 * sizeof(int));
            
    if (ia == NULL) {
           
         printf("Cannot malloc\n");
         exit(1);
    }
        
    for (ip = ia; ip < ia + 50; ip++) {
        
           *ip=randnum(1000);
           printf("%-4d", *ip);
           
           if (ia <= ip) {
            
                printf("%-4d", *ip);
           }
    }
     
    printf("\n");
    free(ia);

}

int randnum(int range) {

    int    v;
    v = rand();
    return (v * range / RAND_MAX + 1);

}

[andyhunter]

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

int randnum(int range);

void main (void) {

    int    *ia, *ip;
    
    srand(time(NULL));
    ia = (int*)malloc (50 * sizeof(int));
            
    if (ia == NULL) {
           
         printf("Cannot malloc\n");
         exit(1);
    }
        
    for (ip = ia; ip < ia + 50; ip++) {
        
           *ip=randnum(1000);
           printf("%-4d", *ip);
    }
	
	printf("\n\n\n"); //newlines
	
	//array backwards
	for(ip--;ip > ia; ip--) {
		printf("%-4d",*ip);
	}
     
    printf("\n");
    free(ia);

}

int randnum(int range) {

    int    v;
    v = rand();
    return (v * range / RAND_MAX + 1);

}

What exactly do you mean by you don't want columns. If you don't want to format the output then remove the -4d format specifier and leave only:

printf("%d", *ip);