Review:   difference in behavior between C and Java in the assignment statement

  • Java will only allow "safe" assignments for number data types: 

           int x;
       double y;

 Allowed:

       y = x;

 Not allowed (without casting):

       x = y;     // Need:  x = (int) y;

  • In contrast, C is always allow assignment of any number type value 

           int x;
       double y;

 Allowed:

       y = x;
       x = y;    // Without casting !

Difference in behavior between C and Java in function invocations using mismatched types

  • The same behavior applies when you invoke a function using values of different data type than specified in the function signature:

    • Java will allow a function call if:

      • The data type of the actual parameter can safely be converted to the data type of the formal parameter

    • C will always allow the function call

      But remember that:

      • C will convert the actual parameter to the data type of the formal parameter if they are different number types

Example function calls that shows the difference between C and Java

  • The following C program will compile and run without casting: 

    

   int square(int x)
   {
      return x*x;
   }

   int main( )
   {
      float a = 4, b;

      b = square(a); // C compiler will convert (float) a to (int) !

      printf("Square of %f = %f\n", a, b);
   }

     

DEMO: demo/C/set1/param1.c

Example function calls that shows the difference between C and Java

  • A same program in Java will have compile errors: 

    public class param1
{
   public static int square(int x)
   {
      return x*x;
   }

   public static void main(String[] args)
   {
      float a = 4, b;

      b = square(a); // Cannot pass a float value ! Need (int) casting

      System.out.printf("Square of %d = %d\n", a, b);
   } 
}

    Java requires casting (int) !

DEMO: demo/C/set1/param1.java