The C99 Standard

  C99 is an informal name for ISO/IEC 9899:1999, a past version of the C programming language standard. The latest standard is called C11. Even though there are standards like C99 and C11, the most widely supported C standard is still ANSI C. Here in this post I am discussing the differences between ANSI C and C99.

• inline, restrict, _Bool, _Complex and _Imaginary are the new keywords introduced by C99.

• _Bool, long long, _Imaginary and _Complex are the new data types included by C99.

• long long has 64 bit precision.

• Declarations can be mixed with other statements.

                     int x;

                     x=10;

                     printf ("\nx is %d",x);

                     int y=20;   //Valid in C99, but error in ANSI C.

• Declarations within for loop is allowed.

                    for(int i=0;i<10;i++)  //Valid in C99, but error in ANSI C.

                    {

                          printf("\nHello");

                    } 

• Variable length arrays are supported in C99.

• Variable length macro arguments are allowed in C99.

• true and false are predefined macro constants in C99.

• Return type is no longer integer by default.

• Unicode characters are supported by C99. \u or \U followed by hexadecimal numbers will print Unicode characters.

• Single line comments ( // ) in C++ are supported by C99.

• Compound literals are supported by C99 which are used instead of temporary arrays used in function calls.