CSC373/406: Lecture 4 (Assembly I (Pointers; Arithmetic))

Similarities

Operators same as Java:

Arithmetic

i = i+1; i++; i--; i *= 2;
+, -, *, /, %

Syntax same as in Java:

if ( ) { } else { }
while ( ) { }
do { } while ( );
for(i=1; i <= 100; i++) { }
switch ( ) {case 1: ... }
continue; break;

Differences

C programs are compiled to machine executable binary code, whereas Java programs are (usually) compiled to Java byte code, and are run by an interpreter.
C exposes more of the underlying computer systems.
C is platform-dependent.
C is not safe; it has powerful pointers.

For loops

  C                             Java
  int i;
  for(i = 0; i < 10; i++) ...   for(int i = 0; i < 10; i++) ...

Array declarations:

  C                             Java
  int a[];                      int[] a;

Array size:

  C                             Java
  ???                           a.size;

Uninitialized variables; catch with -Wall compiler option

int main() {
  int i;
  sqrt(i);
}

Error handling

The compilation system performs the translation of the source file hello.c to an executable hello which consists of a sequence of low-level machine language instructions.
To obtain the preprocessed source program hello.i, do:
```
$ gcc -o hello.i -E hello.c
```
To obtain the assembly program hello.s, do:
```
$ gcc -o hello.s -S hello.c
```
To obtain the binary object file hello.o (similar to java hello.class file), do:
```
$ gcc -o hello.o -c hello.c
```

Revised: 2007/04/05 17:41