Thread: Trying to fill an int array

Originally posted by boojus
I'm trying to fill an integer array with descending values starting at a max of whatever the user enters. so if they enter 5, the array should be a[0]=1, a[1]=2, a[2]=3, a[3]=4, and a[4]=5. the rest of the postions, i forget what they are called, are unimportant, so i guess a[i] has to equal a null? right now its not working. i try to display the array but it doesnt give me the values i was hoping for. anyway here is what i have:

Code:

#include <iostream>
#include <algorithm>
using namespace std;

int main()
{
	char input[4];
	int a[101], numInput, i=0;

	cout << "Enter a number ranging from 9-100: ";
	cin.getline(input, 4);
	numInput = atoi(input);
	while(numInput < 9 || numInput >100)
	{
			cout << "Enter a number ranging from 9-100: ";
			cin.getline(input,4);
			numInput = atoi(input);
	}
/**********THIS PART DOESN'T WORK****************/
	i = numInput;
	while(i>=1)
	{
		a[i-1]=i;
                i--;
	}
	cout << a[i-1]  <<endl;
/**********************************************/


//while( next_permutation( a.begin() , a.end() ) )
{
   //cout << input << endl;
}
return 0;
}

That should work, at least it makes sense in my head!

hmm.
maybe it does work. i guess the array was quite big so when i tried to cout<<a; it was to big maybe and it gave me some weird value. well it does work how i need it to.

cout << a << endl; will output the address of the array a, this is likely not what you wanted. To output an array you can use std::copy like so
std::copy(vints.begin(),vints.end(),std::ostream_i terator<int>(std::cout," "));

where vints is a vector<int>, to do the same thing for an array we note that a pointer to an array is a random access iterator.

std::copy(a,&a[sizeof(a)/sizeof(a[0])],std::ostream_iterator<int>(std::cout," "));

Here we have a pointer to the start of the array and a pointer one past the end. Note that this will NOT work for a dynamically allocated array. You need to keep track of the size yourself and ether pass a pointer to a+size or use copy_n and pass the size as a paramiter.

I usually like to keep something like this around

Code:

template<class InputIterator>
bool write_csv(InputIterator ii, InputIterator end, std::ostream &os=std::cout) {
    os << '{';
    if(ii != end) {
        os << *ii; 
        while(++ii != end) os << ", " << *ii; 
    }
    os << '}';
    return os.good();
}

template<class Container> 
bool write_csv(const Container &c, std::ostream &os=std::cout) {
    return write_csv(c.begin(),c.end(),os);
}

This provides nicely formated comma seperated values for any container, container-like structure, or anything I can get a pair of iterators out of. Finally if you intend to go through every permutation of a 100 element array I Really want to know where you buy your computers.