This a grammar for plain C reformatted from this Yacc file. Tokens are in bold.

TranslationUnit	→	ExternalDecl
	|	TranslationUnitExternalDecl
ExternalDecl	→	FunctionDefinition
	|	Decl
FunctionDefinition	→	DeclSpecsDeclaratorDeclListCompoundStat
	|	DeclaratorDeclListCompoundStat
	|	DeclSpecsDeclaratorCompoundStat
	|	DeclaratorCompoundStat
Decl	→	DeclSpecsInitDeclaratorList;
	|	DeclSpecs;
DeclList	→	Decl
	|	DeclListDecl
DeclSpecs	→	StorageClassSpecDeclSpecs
	|	StorageClassSpec
	|	TypeSpecDeclSpecs
	|	TypeSpec
	|	TypeQualifierDeclSpecs
	|	TypeQualifier
StorageClassSpec	→	auto|register|static|extern|typedef
TypeSpec	→	void|char|short|int|long|float |double|signed|unsigned
	|	StructOrUnionSpec|EnumSpec|TypedefName
TypeQualifier	→	const|volatile
StructOrUnionSpec	→	StructOrUnionId{StructDeclList}
	|	StructOrUnion{StructDeclList}
	|	StructOrUnionId
StructOrUnion	→	struct|union
StructDeclList	→	StructDecl
	|	StructDeclListStructDecl
InitDeclaratorList	→	InitDeclarator
	|	InitDeclaratorList,InitDeclarator
InitDeclarator	→	Declarator
	|	Declarator=Initializer
StructDecl	→	SpecQualifierListStructDeclaratorList;
SpecQualifierList	→	TypeSpecSpecQualifierList
	|	TypeSpec
	|	TypeQualifierSpecQualifierList
	|	TypeQualifier
StructDeclaratorList	→	StructDeclarator
	|	StructDeclaratorList,StructDeclarator
StructDeclarator	→	Declarator
	|	Declarator:ConstExp
	|	:ConstExp
EnumSpec	→	enumId{EnumeratorList}
	|	enum{EnumeratorList}
	|	enumId
EnumeratorList	→	Enumerator
	|	EnumeratorList,Enumerator
Enumerator	→	Id
	|	Id=ConstExp
Declarator	→	PointerDirectDeclarator
	|	DirectDeclarator
DirectDeclarator	→	Id
	|	(Declarator)
	|	DirectDeclarator[ConstExp]
	|	DirectDeclarator[]
	|	DirectDeclarator(ParamTypeList
	|	DirectDeclarator(IdList)
	|	DirectDeclarator()
Pointer	→	*TypeQualifierList
	|	*
	|	*TypeQualifierListPointer
	|	*Pointer
TypeQualifierList	→	TypeQualifier
	|	TypeQualifierListTypeQualifier
ParamTypeList	→	ParamList
	|	ParamList,...
ParamList	→	ParamDecl
	|	ParamList,ParamDecl
ParamDecl	→	DeclSpecsDeclarator
	|	DeclSpecsAbstractDeclarator
	|	DeclSpecs
IdList	→	Id
	|	IdList,Id
Initializer	→	AssignmentExp
	|	{InitializerList}
	|	{InitializerList,}
InitializerList	→	Initializer
	|	InitializerList,Initializer
TypeName	→	SpecQualifierListAbstractDeclarator
	|	SpecQualifierList
AbstractDeclarator	→	Pointer
	|	PointerDirectAbstractDeclarator
	|	DirectAbstractDeclarator
DirectAbstractDeclarator	→	(AbstractDeclarator)
	|	DirectAbstractDeclarator[ConstExp]
	|	[ConstExp]
	|	DirectAbstractDeclarator[]
	|	[]
	|	DirectAbstractDeclarator(ParamTypeList)
	|	(ParamTypeList)
	|	DirectAbstractDeclarator()
	|	()
TypedefName	→	Id
Stat	→	LabeledStat|ExpStat|CompoundStat|SelectionStat| IterationStat|JumpStat
LabeledStat	→	Id:Stat
	|	caseConstExp:Stat
	|	default:Stat
ExpStat	→	Exp;
	|	;
CompoundStat	→	{DeclListStatList}
	|	{StatList}
	|	{DeclList}
	|	{}
StatList	→	Stat
	|	StatListStat
SelectionStat	→	if(Exp)Stat
	|	if(Exp)StatelseStat
	|	switch(Exp)Stat
IterationStat	→	while(Exp)Stat
	|	doStatwhile(Exp);
	|	for(Exp;Exp;Exp)Stat
	|	for(Exp;Exp;)Stat
	|	for(Exp;;Exp)Stat
	|	for(Exp;;)Stat
	|	for(;Exp;Exp)Stat
	|	for(;Exp;)Stat
	|	for(;;Exp)Stat
	|	for(;;)Stat
JumpStat	→	JumpSpec;
JumpSpec	→	gotoId|continue|break|returnExp|return
Exp	→	AssignmentExp
	|	Exp,AssignmentExp
AssignmentExp	→	ConditionalExp
	|	UnaryExpAssignmentOperatorAssignmentExp
AssignmentOperator	→	=|*=|/=|%=|+=|-=|<<=| >>=|&=|^=||=
ConditionalExp	→	LogicalOrExp
	|	LogicalOrExp?Exp:ConditionalExp
ConstExp	→	ConditionalExp
LogicalOrExp	→	LogicalAndExp
	|	LogicalOrExp||LogicalAndExp
LogicalAndExp	→	InclusiveOrExp
	|	LogicalAndExp&&InclusiveOrExp
InclusiveOrExp	→	ExclusiveOrExp
	|	InclusiveOrExp|ExclusiveOrExp
ExclusiveOrExp	→	AndExp
	|	ExclusiveOrExp^AndExp
AndExp	→	EqualityExp
	|	AndExp&EqualityExp
EqualityExp	→	RelationalExp
	|	EqualityExp==RelationalExp
	|	EqualityExp!=RelationalExp
RelationalExp	→	ShiftExpression
	|	RelationalExp<ShiftExpression
	|	RelationalExp>ShiftExpression
	|	RelationalExp<=ShiftExpression
	|	RelationalExp>=ShiftExpression
ShiftExpression	→	AdditiveExp
	|	ShiftExpression<<AdditiveExp
	|	ShiftExpression>>AdditiveExp
AdditiveExp	→	MultExp
	|	AdditiveExp+MultExp
	|	AdditiveExp-MultExp
MultExp	→	CastExp
	|	MultExp*CastExp
	|	MultExp/CastExp
	|	MultExp%CastExp
CastExp	→	UnaryExp
	|	(TypeName)CastExp
UnaryExp	→	PostfixExp
	|	++UnaryExp
	|	--UnaryExp
	|	UnaryOperatorCastExp
	|	sizeofUnaryExp
	|	sizeof(TypeName)
UnaryOperator	→	&|*|+|-|~|!
PostfixExp	→	PrimaryExp
	|	PostfixExp[Exp]
	|	PostfixExp(ArgumentExpList)
	|	PostfixExp()
	|	PostfixExp.Id
	|	PostfixExp->Id
	|	PostfixExp++
	|	PostfixExp--
PrimaryExp	→	Id|IntConst|FloatConst| EnumerationConst|StringConst| (Exp)
ArgumentExpList	→	AssignmentExp
	|	ArgumentExpList,AssignmentExp

Nothing Helps

In the above grammar, the replacement is always a non-empty string. Right sides may be empty, usually written as ε. A rule can then take the form Whatever→ε, meaning that the non-terminal Whatever is allowed to just disappear during a derivation. This can simplify certain things. For instance, the C for statement may omit any of the initialization, test, or increment parts of the header. In the above, this is represented by giving eight versions of the for header, with each combination of presence or omission. But using an epsilon rule, we can write this more concisely.

IterationStat	→	while(Exp)Stat
	|	doStatwhile(Exp);
	|	for(OptExp;OptExp;OptExp)Stat
OptExp	→	Exp|ε

Epsilon may help in other places as well, but this seems the most dramatic.