Add calculator challenge

README.md

@@ -37,6 +37,7 @@ Follow me on [https://packagemain.tech](packagemain.tech) to read other stuff I
  - [x] ([@shogg](https://github.com/shogg)) [nasacollage](https://github.com/plutov/practice-go/tree/master/nasacollage)
 - [x] ([@shogg](https://github.com/shogg)) [node_degree](https://github.com/plutov/practice-go/tree/master/node_degree)
 - [ ] [compression](https://github.com/plutov/practice-go/tree/master/compression)
+- [ ] [calculator](https://github.com/plutov/practice-go/tree/master/calculator)
 
 ### Run tests with benchmarks
 

calculator/README.md

@@ -0,0 +1,31 @@
+### Calculator
+
+Create a calculator that can evaluate simple mathematical expressions. The calculator should be able to handle the basic arithmetic operations: addition, subtraction, multiplication, and division.
+
+### Function
+
+```go
+Eval(expr string) (float64, error)
+```
+
+### Examples
+
+```go
+result, err := Eval("1 + 2")
+fmt.Println(result) // 3
+
+result, err := Eval("2 * 3")
+fmt.Println(result) // 6
+
+result, err := Eval("10 / 2 + 6")
+fmt.Println(result) // 11
+
+result, err := Eval("( 2 + 3 ) * 4")
+fmt.Println(result) // 20
+```
+
+### Run tests with benchmarks
+
+```
+go test -bench .
+```

calculator/calculator.go

@@ -0,0 +1,5 @@
+package calculator
+
+func Eval(expr string) (float64, error) {
+	return 3.0, nil
+}

calculator/calculator_test.go

@@ -0,0 +1,38 @@
+package calculator
+
+import "testing"
+
+var tests = []struct {
+	expr     string
+	result   float64
+	isErrNil bool
+}{
+	{"1 + 2", 3.0, true},
+	{"(2 + 1) - (-3) * 4", 15.0, true},
+	{"(2 + 1) - (-3) * 4 +", 0.0, false},
+	{"", 0.0, false},
+	{"1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10", 55.0, true},
+	{"() + ()", 0.0, false},
+	{"(1 + 2) + (3 + 4)", 10.0, true},
+	{"((5 - 2) * 3 + 1) / ((3 + 1) - 2)", 5.0, true},
+}
+
+func TestEval(t *testing.T) {
+	for _, tt := range tests {
+		t.Run(tt.expr, func(t *testing.T) {
+			result, err := Eval(tt.expr)
+			if result != tt.result {
+				t.Errorf("Eval(%s) got %f, want %f", tt.expr, result, tt.result)
+			}
+			if (err == nil) != tt.isErrNil {
+				t.Errorf("Eval(%s) got error %v, want error %v", tt.expr, err, tt.isErrNil)
+			}
+		})
+	}
+}
+
+func BenchmarkEval(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		Eval("(2 + (1)) - (-3) * 4")
+	}
+}