difference between c99 and c11 [closed]

Answer 1

Per the C 2011 standard itself, here are the major changes from C99:

Foreword
...
6     This third edition cancels and replaces the second edition, ISO/IEC 9899:1999, as corrected by ISO/IEC 9899:1999/Cor 1:2001, ISO/IEC 9899:1999/Cor 2:2004, and ISO/IEC 9899:1999/Cor 3:2007. Major changes from the previous edition include:

     — conditional (optional) features (including some that were previously mandatory)

     — support for multiple threads of execution including an improved memory sequencing model, atomic objects, and thread-local storage ( and )

     — additional floating-point characteristic macros ()

     — querying and specifying alignment of objects (, )

     — Unicode characters and strings () (originally specified in ISO/IEC TR 19769:2004)

     — type-generic expressions

     — static assertions

     — anonymous structures and unions

     — no-return functions

     — macros to create complex numbers ()

     — support for opening files for exclusive access

     — removed the gets function ()

     — added the aligned_alloc, at_quick_exit, and quick_exit functions ()

     — (conditional) support for bounds-checking interfaces (originally specified in ISO/IEC TR 24731−1:2007)

     — (conditional) support for analyzability