# C 程序：检查数字是正数还是负数 > 原文： [https://www.programiz.com/c-programming/examples/negative-positive-zero](https://www.programiz.com/c-programming/examples/negative-positive-zero) #### 在此示例中，您将学习检查数字（由用户输入）是负数还是正数。 要理解此示例，您应该了解以下 [C 编程](/c-programming "C tutorial")主题： * [C 编程运算符](/c-programming/c-operators) * [C `if...else`语句](/c-programming/c-if-else-statement) * * * 该程序从用户那里获取一个号码，并检查该号码是`positive`还是`negative`或`zero`。 * * * ## 使用`if...else`检查正负 ```c #include <stdio.h> int main() { double num; printf("Enter a number: "); scanf("%lf", &num); if (num <= 0.0) { if (num == 0.0) printf("You entered 0."); else printf("You entered a negative number."); } else printf("You entered a positive number."); return 0; } ``` 您还可以使用[嵌套](https://www.programiz.com/c-programming/c-if-else-statement) `if else` [语句](https://www.programiz.com/c-programming/c-if-else-statement)来解决此问题。 * * * ## 使用嵌套`if else`检查正数或负数 ```c #include <stdio.h> int main() { double num; printf("Enter a number: "); scanf("%lf", &num); if (num < 0.0) printf("You entered a negative number."); else if (num > 0.0) printf("You entered a positive number."); else printf("You entered 0."); return 0; } ``` * * * **输出 1** ```c Enter a number: 12.3 You entered a positive number. ``` **输出 2** ```c Enter a number: 0 You entered 0. ```