GCC useful flags for compiling ANSI C and C++

Those flags can be used when running GCC to compile C and C++ source code

for example:

gcc -Wall -Wredundant-decls -Wundef source.c -o opt

flags :

-Wredundant-decls
-Wundef
-Wfloat-equal
-Wunreachable-code
-Wmissing-declarations
-Wmain
-pedantic
-Wextra
-Wall
-Wformat=2
-Wunused-parameter
-Wsign-compare
-Wconversion
-Wsequence-point
-Wdeclaration-after-statement // C and ObjC Only
-Wundef -Wpointer-arith
-Wnested-externs // C and ObjC Only
-Wfloat-conversion