implicit declaration of function getchar(...)?

Code:

---

#include <conio.h>
#include <iostream.h>
int prime(int n)
    {
    int i;
    if (n % 2 == 0)
    return (n==2);
    if (n % 3 == 0)
    return (n==3);
    if (n % 5 == 0)
    return (n==5);
    for (i=7; i*i <= n; i+=2)
    if (n % i == 0)
    return 0;
    return 1;
}

void main(void)
    {
    int i, n;
    n = 1000;
    clrscr();
    cout << "ENTER THE NUMBER :-";
    cin >> i;
    if (prime(i))
    cout <<"\n THE NUMBER IS PRIME.";
    else
    cout << "\nTHE NUMBER IS NOT PRIME.";
    getch();
}

---

it gives me the error 'implicit declaration of function getchar(...)'what does it mean?

Your prime() function should return bool, not int. Use the standard headers <XXXX>, not <XXXX.h>. You really don't need getchar() here.

Code:

---

#include <conio.h>
#include <iostream>
#include<cstdlib>
bool prime(int n)
    {
    int i;
    if (n % 2 == 0)
    return (n==2);
    if (n % 3 == 0)
    return (n==3);
    if (n % 5 == 0)
    return (n==5);
    for (i=7; i*i <= n; i+=2)
    if (n % i == 0)
    return 0;
    return 1;
}

void main()
    {
    int i, n;
    n = 1000;
    cout << "ENTER THE NUMBER :-";
    cin >> i;
    if (prime(i))
    cout <<"\n THE NUMBER IS PRIME.";
    else
    cout << "\nTHE NUMBER IS NOT PRIME.";
    system("PAUSE");
    return 0;
}

---

Thanku it works now. But y? it gives me the error with clrscr(); and getch(); ?

Those two functions are non-standard, so I don't bother using them.

There are still a few problems with your code. Most notably, change main()'s return type to int before you get flamed. Also, some better indenting would help.

You're using Dev-C++, right?
Basically, Dev-C++ uses the MinGW port of GCC as its default compiler, and GCC doesnt support conio.h (well), since that is more for Borland's compilers.
However, since you dont even need conio.h in your program, you can just take it out, e.g.

Code:

---

#include <iostream>
#include <cstdlib>

using std::cout;
using std::cin;

bool prime(int n)
{
        if (n % 2 == 0)
                return (n == 2);
        if (n % 3 == 0)
                return (n == 3);
        if (n % 5 == 0)
                return (n == 5);
        for (i = 7; i * i <= n; i += 2)
                if (n % i == 0)
                        return 0;
        return 1;
}

int main()
{
        int i;
        cout << "ENTER THE NUMBER :-";
        cin >> i;
        if (prime(i))
                cout <<"\n THE NUMBER IS PRIME.";
        else
                cout << "\nTHE NUMBER IS NOT PRIME.";
        system("PAUSE");
        return 0;
}

---

thanku