C :

#include<stdio.h>
int main() 
{
    int i = 0, oldNumber, newNumber = 0;
    scanf("%d", &oldNumber);
    while(oldNumber != 0)
	{
        newNumber *= 10;
        newNumber += oldNumber % 10;
        oldNumber /= 10;
    }
    printf("%d\n", newNumber);
    return 0;
}

C++ :

#include<cstdlib>
#include<cstdio>
#include<iostream>
#include<cstring>
using namespace std;
int main()
{
	char s[100];
	char a[100];
	int N;
	cin>>N;
	sprintf(s,"%d",N);
	int n=strlen(s);
	for(int i=0;i<=n-1;++i)
	  a[n-i-1]=s[i];
	if(N<0)
	  cout<<"-";
	sscanf(a,"%d",&N);
	cout<<N;
	//system("pause");
	return 0;

}

Pascal :

var
st:string;
t:char;
flag:boolean;
len,i:longint;
begin
readln(st);
if st[1] = '-' then
begin
flag:=true;
delete(st,1,1);
end
else flag := false;
len := length(st);
for i := 1 to len div 2 do
begin
t := st[i];
st[i] := st[len - i + 1];
st[len - i + 1] := t;
end;
while (st[1] = '0') and (length(st) > 1) do delete(st,1,1);
if flag then st := '-' + st;
writeln(st);
end.