checker: use ++ / -- instead of += 1 / -= 1

vlib/strconv/ftoa/f64_str.v

@@ -110,8 +110,8 @@ fn (d Dec64) get_string_64(neg bool, i_n_digit int, i_pad_digit int) string {
 		out /= ten_pow_table_64[out_len - n_digit ]
 		//println("out1:[$out] ${d.m / ten_pow_table_64[out_len - n_digit ]}")
 		if d.m / ten_pow_table_64[out_len - n_digit ] < out {
-			d_exp += 1
-			n_digit += 1
+			d_exp++
+			n_digit++
 		}
 
 		//println("cmp: ${d.m/ten_pow_table_64[out_len - n_digit ]} ${out/ten_pow_table_64[out_len - n_digit ]}")

vlib/v/checker/checker.v

@@ -709,6 +709,9 @@ fn (mut c Checker) assign_expr(mut assign_expr ast.AssignExpr) {
 			} else if !right.is_number() && right_type != table.string_type && !right.is_pointer() {
 				c.error('operator += not defined on right operand type `$right.name`', assign_expr.val.position())
 			}
+			if assign_expr.val is ast.IntegerLiteral && assign_expr.val.str().int() == 1 {
+				c.error('use `++` instead of `+= 1`', assign_expr.pos)
+			}
 		}
 		.minus_assign {
 			if !left.is_number() && !left.is_pointer() {
@@ -716,6 +719,9 @@ fn (mut c Checker) assign_expr(mut assign_expr ast.AssignExpr) {
 			} else if !right.is_number() && !right.is_pointer() {
 				c.error('operator -= not defined on right operand type `$right.name`', assign_expr.val.position())
 			}
+			if assign_expr.val is ast.IntegerLiteral && assign_expr.val.str().int() == 1 {
+				c.error('use `--` instead of `-= 1`', assign_expr.pos)
+			}
 		}
 		.mult_assign, .div_assign {
 			if !left.is_number() {

vlib/v/checker/checker_test.v

@@ -55,7 +55,7 @@ fn check_path(vexe, dir, voptions, result_extension string, tests []string) int
 			println('found:')
 			println(found)
 			println('============\n')
-			nb_fail += 1
+			nb_fail++
 		} else {
 			println(term.green('OK'))
 			os.rm(program)

vlib/v/checker/tests/plus_or_minus_assign_one_err.out

@@ -0,0 +1,13 @@
+vlib/v/checker/tests/plus_or_minus_assign_one_err.v:3:6: error: use `++` instead of `+= 1`
+    1 | fn main() {
+    2 |     mut foo := 10
+    3 |     foo += 1
+      |         ~~
+    4 |     foo -= 1
+    5 | }
+vlib/v/checker/tests/plus_or_minus_assign_one_err.v:4:6: error: use `--` instead of `-= 1`
+    2 |     mut foo := 10
+    3 |     foo += 1
+    4 |     foo -= 1
+      |         ~~
+    5 | }

vlib/v/checker/tests/plus_or_minus_assign_one_err.vv

@@ -0,0 +1,5 @@
+fn main() {
+	mut foo := 10
+	foo += 1
+	foo -= 1
+}

vlib/v/tests/option_test.v

@@ -167,7 +167,7 @@ fn test_reassignment() {
 	assert x2 == 777
 	x2 = 100
 	assert x2 == 100
-	x2 += 1
+	x2++
 	assert x2 == 101
 	//
 	mut x3 := 0