判断结构

```javascript
var mid = 25;
var high = 50;
var low =1;
var current = 13;
var found = -1;
if (current < mid) {
mid = (current - low) / 2;
console.log(mid); //6
}

var mid = 25;
var high = 50;
var low =1;
var current = 13;
var found = -1;
if (current < mid) {
mid = (current - low) / 2;
console.log(mid);
} else {
mid = (current + high) / 2;
console.log(mid);
}

var mid = 25;
var high = 50;
var low =1;
var current = 13;
var found = -1;
if (current < mid) {
mid = (current - low) / 2;
console.log(mid);
} else if (current > mid) {
mid = (current + high) / 2;
} else {
found = current;
console.log(found);
}