C/C++ and Java Language Comparisons

Much of the programming fundamentals learned in your Java software development classes apply directly to programming in the C language.

• The C language was developed at AT & T in the early 1970s.
  • C is still very popular in a number of domains including operating system development and embedded systems.
  • Compiler generates machine code that runs on specific microcontrollers.
• The C++ language was developed at Bell Labs in 1979 (originally named “C with Classes”).
  • Attempts to be backwards compatible with C.
  • Adds a number of features including object oriented constructs like user defined classes.
  • Compiler generates machine code that runs on specific microcontrollers.
• Java was developed at Sun Microsystems and released in 1995.
  • Was designed so that C/C++ developers could quickly learn.
  • Uses very similar syntax as C/C++.
  • Compiler produces byte code that runs on a Java Virtual Machine.
  • Includes a number of language “improvements” over C++.
• C# was developed at Microsoft beginning in 1999.
  • Similar to Java but compiler produces byte code (termed Common Intermediate Language) that runs on the .NET runtime.
  • Includes a number of language “improvements” over Java.

Our discussion will be based a specific variant of C know as C99 (as implemented by the GNU GCC compiler).

C provides numeric data types that are similar to those in Java.

In Java we have the following numeric data primitives:

In C, the space required by the int and long types depends on the target microcontroller. Also, we have some additional numeric data types:

The C99 standard introduces the following types which have a fixed space requirement. You should use these types in your code:

Java supports a few other primitive data types:

• boolean – Represents true or false.
• char – holds a single character, a multi-byte Unicode character.

C language differences:

• C++ has support for a Boolean type (called bool) but C does not.
• C99 has support for a Boolean type (called _Bool).
• C99 adds additional types like _Complex and _Imaginary; however we likely won't use these.
• C/C++ has the char data type:
  • Similar to Java in that it stores a single character.
  • Differs from Java in that it is 8-bits big and just stores the ASCII value of the character.
• Although not a primitive type, Java supports the string class.
• Storage of multiple character strings in C is typically done with null-terminated character arrays.
• Such a character array is referred to as a C-style string.
• The following code allocates space for eight bytes (the seven characters and a null character that is used to terminate the string).

char word[] = "funness";

• When a variable is declared, memory is allocated for the variable.
  • Typically a local variable will be placed on the stack; however the compiler may choose to dedicate a specific register to store the variable.
  • If the variable is not given a value when it is declared…
    • In Java, the variable is initialized to 0.
    • In C/C++, no initialization is performed. Make sure you initialize variables when you declare them. Otherwise your program may behave unpredictablly.
    • Exceptions:
      • Uninitialized global and static variables are given initial values of 0.
      • Some debuggers may initialize variables that are not explicitly initialized (which can be even more frustrating to debug because you don't see the problem when debugging).

• Looping constructs in C are identical to those in Java:
  • for() loops.
  • while() loops.
  • do {} while() loops.
• Conditional constructs in C are identical to those in Java:
  • if() statements.
  • if() {} else {} statements.
  • switch() statements.

• C/C++ and Java share the same arithmetic operators.
• C/C++ and Java share the same operator precedence rules.
• C/C++ and Java share the same arithmetic promotion rules:
  • For unary operations, if the operand is byte or short, it gets converted to int.
  • For binary operations:
    • If either operand is a double, then the other operand is converted to a double,
    • Otherwise, if either operand is a float, then the other operand is converted to a float,
    • Otherwise, if either operand is a long, then the other operand is converted to a long,
    • Otherwise, both operands are converted to an int.