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1-js/4-data-structures/7-array/5-array-input-sum/solution.md

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+Please note the subtle, but important detail of the solution. We don't convert `value` to number instantly after `prompt`, because after `value = +value` we would not be able to tell an empty string (stop sign) from the zero (valid number). We do it later instead.
+
+
+```js run demo
+function sumInput() {
+ 
+  let numbers = [];
+
+  while (true) {
+
+    let value = prompt("A number please?", 0);
+
+    // should we cancel?
+    if (value === "" || value === null || !isFinite(value)) break;
+
+    numbers.push(+value);
+  }
+
+  let sum = 0;
+  for (let number of numbers) {
+    sum += number;
+  }
+}
+
+alert( sumInput() ); 
+```
+