C :

#include<stdio.h>
#include<string.h>
int main()
{
    char a[300];
    int i=-1;
    gets(a);
    while(a[++i]!='\0')
    {
        if(a[i]=='a'||a[i]=='e'||a[i]=='i'||a[i]=='o'||a[i]=='u')
            putchar(a[i]);
    }
    puts("");
    return 0;
}

C++ :

#include<iostream>
#include<string.h>
using namespace std;
int main()
{
    char a[50],b[50],c,d=0;
    cin>>a;
    c=strlen(a);
    while(c--)
        if(a[c]=='a'||a[c]=='e'||a[c]=='i'||a[c]=='o'||a[c]=='u')
            b[d]=a[c],d++;
    while(d--)
        cout<<b[d];
}

Pascal :

var st:string;
    i:longint;
begin
  readln(st);
  for i:=1 to length(st) do
  if (st[i]='a') or (st[i]='e') or  (st[i]='i') or (st[i]='o') or  (st[i]='u') then write(st[i]);
end.