scanf in c

/* scanf example */
#include <stdio.h>

int main ()
{
  char str [80];
  int i;

  printf ("Enter your family name: ");
  scanf ("%79s",str);  
  printf ("Enter your age: ");
  scanf ("%d",&i);
  printf ("Mr. %s , %d years old.\n",str,i);
  printf ("Enter a hexadecimal number: ");
  scanf ("%x",&i);
  printf ("You have entered %#x (%d).\n",i,i);
  
  return 0;
}

#include <stdio.h>

int main () {
   scanf("%s", str);
   printf("%s"str);
   scanf("%d", int);
   printf("%d"int);
   return(0);
}

scanf("%d", &b);

#include <stdio.h>
int main()
{
    int a;
    float b;

    printf("Enter integer and then a float: ");
  
    // Taking multiple inputs
    scanf("%d%f", &a, &b);

    printf("You entered %d and %f", a, b);  
    return 0;
}

scanf("%d",&int);