Automatic type conversion in function calls

Automatic type conversions are performed in a function call

C's conversion rule:

If mismatched data types are used in a function call in C:

In other words:

The C compiler will always perform the necessary conversions to make the data types match
Even if the conversion will result in loss of accuracy !!!

Example:

float f( float x) { float r; r = x*x; return(r); } int main(int argc, char *argv[] ) { int a, b; a = 2; b = f(a); }

In the function call:

b = f(a)
The compiler will: (1) convert the int representation in variable a to a float representation (2) convert the return value from float representation to an int representation

To show you that these conversion indeed takes place, I have added a number of printBits( ) calls to show the binary representation of the variables:

#include <stdio.h> float f( float x) { printf(" f: x = %f , in binary: ", x); printBits(&x); printf("\n"); float r; r = x*x; printf(" f: r = %f , in binary: ", r); printBits(&r); printf("\n"); return(r); } int main(int argc, char *argv[] ) { int a, b; a = 2; printf("main: a = %d , in binary: ", a); printBits(&a); printf("\n"); b = f(a); printf("main: b = %d , in binary: ", b); printBits(&b); printf("\n\n"); }

Output:

main: a = 2 , in binary: 00000000000000000000000000000010 (int repr of 2) f: x = 2.000000 , in binary: 01000000000000000000000000000000 (float repr of 2) f: r = 4.000000 , in binary: 01000000100000000000000000000000 (float repr of 4) main: b = 4 , in binary: 00000000000000000000000000000100 (int repr of 4)

Example Program: (Demo above code)
- Prog file: /home/cs255001/demo/C/func-call-conv1.c
How to run the program:

Java's behavior in function calls

Java's behavior in a function call is the same as C's behavior, except (due to its nanny property):

If mismatched data types are used in a function call in Java, then:

Example 1: Java will perform safe conversions automatically (= without a cast operator)

public class func_call_conv1 { static int f( float x) { System.out.printf(" f: x = %f , in binary: ", x); printBitFloat(x); System.out.println(); int r; r = (int) (x*x); System.out.printf(" f: r = %d , in binary: ", r); printBitInt(r); System.out.println("\n"); return(r); } public static void main(String[] args) { int a; float b; a = 2; System.out.printf("main: a = %d , in binary: ", a); printBitInt(a); System.out.println("\n"); b = f(a); // Compiler performs these conversions: // int a ---> float x (safe !) // int return value ---> float b (safe !) System.out.printf("main: b = %f , in binary: ", b); printBitFloat(b); System.out.println("\n"); } .... // Conversion methods omitted }

Output:

main: a = 2 , in binary: 00000000000000000000000000000010 f: x = 2.000000 , in binary: 01000000000000000000000000000000 f: r = 4 , in binary: 00000000000000000000000000000100 main: b = 4.000000 , in binary: 01000000100000000000000000000000

Example Program: (Demo above code)
- Prog file: /home/cs255001/demo/C/set1/func_call_conv1.java
How to run the program:

Example 2: The Java compiler requires casting to perform unsafe conversions

public class func_call_conv2 { static float f( int x) { System.out.printf(" f: x = %d , in binary: ", x); printBitInt(x); System.out.println(); float r; r = x*x; System.out.printf(" f: r = %f , in binary: ", r); printBitFloat(r); System.out.println("\n"); return(r); } public static void main(String[] args) { float a; int b; a = 2.0f; System.out.printf("main: a = %f , in binary: ", a); printBitFloat(a); System.out.println("\n"); b = (int) f((int) a); // *** Need 2 casts !!! // You need to request explicit casting for // float a --> int x (unsafe !) // float return value --> int b (unsafe !) System.out.printf("main: b = %d , in binary: ", b); printBitInt(b); System.out.println("\n"); } // Conversion methods omitted.... }

Output:

main: a = 2.000000 , in binary: 01000000000000000000000000000000 f: x = 2 , in binary: 00000000000000000000000000000010 f: r = 4.000000 , in binary: 01000000100000000000000000000000 main: b = 4 , in binary: 00000000000000000000000000000100

Example Program: (Demo above code)
- Prog file: /home/cs255001/demo/C/set1/func_call_conv2.java
How to run the program: