#include<stdio.h>
#include<conio.h>
#include<string.h>
char letra;
main()
{printf("Elige una opcion: a=Naturales, b=Pares, c=Impares, d=Negativos, e=Salir ");
letra=getchar();
getchar();
switch(letra)
{
case'a': gotoxy(1,5);
puts("1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25");
break;
case'b': gotoxy(1,5);
puts("2,4,6,8,10,12,14,16,18,20,22,24,26,28,30,32,34,36,38,40,42,44,46,48,50");
break;
case'c': gotoxy(1,5);
puts("1,3,5,7,9,11,13,15,17,19,21,23,25,27,29,31,33,35,37,39,41,43,45,47,49,51");
break;
case'd': gotoxy(1,5);
puts("-1,-2,-3,-4,-5,-6,-7,-8,-9,-10,-11,-12,-13,-14,-15,-16,-17,-18,-19,-20,-21,-22,-23,-24,-25");
break;
}
getchar();
}