int _tmain(int argc, _TCHAR* argv[])
{
    int is=0,in,i=0;
    printf("nhap vao so n: ");
    scanf("%d",&in);
    while(i++ < in)
    {
        if (i<in)
            printf("%d<%d\n\n",i,in);
        printf("i la: %d\n",i);
        printf("is la: %d + %d = ",is, i);
        is = is + i;
        printf("%d\n\n",is);
    }

    return 0;
}