try yourself |run program

#include <stdio.h> 
#include <conio.h> 
void main(){
int age;
clrscr();
again:
printf("\nenter age: ");
scanf("%d",&age);
if(age<18){
printf("\n Not eligible for vote");
goto again;
}
else{
printf("\n Eligible for vote");
}
getch();
}

Program Output

enter age: 15
Not eligible for vote
enter age: 21
Eligible for vote