- Just like Java:
- You can only perform operations of 2 values of the same data type
- Example:
float A, B, C; - Defines 3 float variables A = 4; B = 5; C = A + B;
This is the similar situation as "adding apples and apples".
- Just like Java:
- Operations using values of the different data type must first convert one type into the other before the operation can be performed.
- Example:
int A; - Defines integer float B, C; - Defines 2 float variables A = 4; // Integer B = 5; // Float C = A + B; - The value of A is converted to FLOAT first - Then the addition is performed
This is the similar situation as "adding apples and oranges". We must convert the apples to oranges first before we can add
- Data conversion must take place in the following
operations involving
different data types:
- Binary (arithmethic) operations
Example:
int a; float b; a + b // a in converted to a float
- Assignment operations
Example:
int a; float b; a = b ; // b in converted to a intNote:
- Yes, this is
allowed in
C
- In Java, you need to use
casting:
a = (int) b; // Because b is float !
- Yes, this is
allowed in
C
- Binary (arithmethic) operations
- Fact:
- C was
designed
to write the
UNIX operating system
(they used to write
operating systems in
assembler code !!!)
- The designer of
C has
included many
features to make
system programming
easy
- But these features can also cause major pain (harm) to programmers that do not fully understand its effects !!!
- C was
designed
to write the
UNIX operating system
(they used to write
operating systems in
assembler code !!!)
- Your first feature:
- C will
always
perform
an assignment operation
with
automatic (= "implicit")
type conversion
on ordinary data types
- Even when the type conversion results in loss of accuracy
(That's because Ritchie wants type less so he can write program faster... (he knows that you need to cast (= convert))
Example:
int main(int argc, char* argv[] ) { int i; short s; double d; i = 9827563; s = i; /* Unsafe conversion, allowed in C !!! */ printf( "i = %d , s = %d \n", i, s ); d = 9827563.444; i = d; /* Unsafe conversion, allowed in C !!! */ printf( "d = %lf , i = %d \n", d, i ); d = 9827563.444; s = d; /* Unsafe conversion, allowed in C !!! */ printf( "d = %lf , s = %d \n", d, s ); }
- C will
always
perform
an assignment operation
with
automatic (= "implicit")
type conversion
on ordinary data types
- Example Program:
(Demo above code)
- Prog file: /home/cs255001/demo/C/casting1.c
How to run the program:
- To compile: gcc casting1.c
- To run: ./a.out