C 99 vs. ANSI C

For further information refer to http://www.open-std.org/jtc1/sc22/WG14/www/docs/n1256.pdf

• Restricted pointers: http://gcc.gnu.org/onlinedocs/gcc/Restricted-Pointers.html
• Variable-length arrays: http://gcc.gnu.org/onlinedocs/gcc/Variable-Length.html
• Flexible array members: http://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
• static and type qualifiers in parameter array declarators.
• long long int type:http://gcc.gnu.org/onlinedocs/gcc/Long-Long.html
• Additional floating-point characteristics in <float.h>.
• Removed implicit int.
• Reliable integer division.
• Universal character names (\\u and \\U).
• Compound literals:http://gcc.gnu.org/onlinedocs/gcc/Compound-Literals.html
• Non-constant initializers:http://gcc.gnu.org/onlinedocs/gcc/Initializers.html
• Designated initializers:http://gcc.gnu.org/onlinedocs/gcc/Designated-Inits.html
• // comments:http://gcc.gnu.org/onlinedocs/gcc/C_002b_002b-Comments.html
• Extended integer types and library functions in <inttypes.h> and <stdint.h>.
• Removed implicit function declaration.
• Preprocessor arithmetic done in intmax_t/uintmax_t.
• Mixed declarations and code:http://gcc.gnu.org/onlinedocs/gcc/Mixed-Declarations.html
• New block scopes for selection and iteration statements.
• Integer constant type rules.
• Integer promotion rules.
• Macros with a variable number of arguments.
• The vscanf family of functions in <stdio.h> and <wchar.h>.
• Additional math library functions in <math.h>.
• Floating-point environment access in:code:<fenv.h>.
• IEC 60559 (also known as IEC 559 or IEEE arithmetic) support.
• Trailing comma allowed in enum declaration.
• %lf conversion specifier allowed in printf.
• Inline functions.
• The snprintf family of functions in <stdio.h>.
• Boolean type in <stdbool.h>.
• Empty macro arguments.
• New struct type compatibility rules (tag compatibility).
• Additional predefined macro names.
• _Prama preprocessing operator.
• Standard pragmas.
• __func__ predefined identifier.
• va_copy macro.
• Additional strftime conversion specifiers.
• Deprecate ungetc at the beginning of a binary file.
• Removed deprecation of aliased array parameters.
• Conversion of array to pointer not limited to values.
• Relaxed constraints on aggregate and union initialization.
• return without expression not permitted in function that returns a value (and vice versa).