cgen: fix C style loops without an init; fix integer consts

vlib/v/ast/ast.v

@@ -385,6 +385,7 @@ pub:
 pub struct ForCStmt {
 pub:
 	init     Stmt // i := 0;
+	has_init bool
 	cond     Expr // i < 10;
 	// inc   Stmt // i++;
 	inc      Expr // i++;

vlib/v/gen/cgen.v

@@ -187,8 +187,12 @@ fn (g mut Gen) stmt(node ast.Stmt) {
 		}
 		ast.ForCStmt {
 			g.write('for (')
+			if !it.has_init {
+				g.write('; ')
+			}
+			else {
 				g.stmt(it.init)
-			// g.write('; ')
+			}
 			g.expr(it.cond)
 			g.write('; ')
 			// g.stmt(it.inc)
@@ -925,9 +929,15 @@ fn (g mut Gen) const_decl(node ast.ConstDecl) {
 			// Do not do this when building a module, otherwise the consts
 			// will not be accessible.
 			ast.CharLiteral, ast.IntegerLiteral {
-				g.write('#define $name ')
+				g.definitions.write('#define $name ')
+				// TODO hack. Cut the generated value and paste it into definitions.
+				g.write('//')
+				pos := g.out.len
 				g.expr(expr)
 				g.writeln('')
+				val := string(g.out.buf[pos..])
+				// g.out.go_back(val.len)
+				g.definitions.write(val)
 			}
 			else {
 				styp := g.typ(field.typ)

vlib/v/gen/tests/1.c

@@ -15,6 +15,7 @@ typedef struct {
 	string arg1;
 } multi_return_int_string;
 // end of definitions #endif
+#define pi 3
 int pi2; // inited later
 void foo(int a);
 void User_inc_age(User* u, int n);
@@ -27,10 +28,14 @@ void variadic(variadic_int a);
 void ensure_cap(int required, int cap);
 void println(string s);
 void matches();
+#define path_sep 10
 void end();
+#define localmod__pub_int_const 20
 void localmod__pub_foo();
 int localmod__get_int_10();
-#define pi 3
+
+//3
+
 
 typedef enum {
 	Color_red, // 0
@@ -165,7 +170,7 @@ void matches() {
 	;
 }
 
-#define path_sep 10
+//10
 
 void end() {
 	int i = 2;
@@ -174,7 +179,7 @@ void end() {
 	int e = 2 + 3 * 4;
 }
 
-#define localmod__pub_int_const 20
+//20
 
 void localmod__pub_foo() {
 	int a = 10;

vlib/v/parser/parser.v

@@ -998,8 +998,10 @@ fn (p mut Parser) for_statement() ast.Stmt {
 		mut cond := ast.Expr{}
 		// mut inc := ast.Stmt{}
 		mut inc := ast.Expr{}
+		mut has_init := false
 		if p.peek_tok.kind in [.assign, .decl_assign] {
 			init = p.assign_stmt()
+			has_init = true
 		}
 		else if p.tok.kind != .semicolon {}
 		// allow `for ;; i++ {`
@@ -1026,6 +1028,7 @@ fn (p mut Parser) for_statement() ast.Stmt {
 		p.close_scope()
 		return ast.ForCStmt{
 			stmts: stmts
+			has_init: has_init
 			init: init
 			cond: cond
 			inc: inc