# C 程序：交換兩個數字 > 原文： [https://www.programiz.com/c-programming/examples/swapping](https://www.programiz.com/c-programming/examples/swapping) #### 在此示例中，您將學習使用兩種不同的技術在 C 編程中交換兩個數字。 要理解此示例，您應該了解以下 [C 編程](/c-programming "C tutorial")主題： * [C 數據類型](/c-programming/c-data-types) * [C 編程運算符](/c-programming/c-operators) * [C 輸入輸出（I/O）](/c-programming/c-input-output) * * * ## 使用臨時變量交換數字 ```c #include<stdio.h> int main() { double first, second, temp; printf("Enter first number: "); scanf("%lf", &first); printf("Enter second number: "); scanf("%lf", &second); // Value of first is assigned to temp temp = first; // Value of second is assigned to first first = second; // Value of temp (initial value of first) is assigned to second second = temp; printf("\nAfter swapping, firstNumber = %.2lf\n", first); printf("After swapping, secondNumber = %.2lf", second); return 0; } ``` **輸出** ```c Enter first number: 1.20 Enter second number: 2.45 After swapping, firstNumber = 2.45 After swapping, secondNumber = 1.20 ``` 在上述程序中，為`temp`變量分配了`first`變量的值。 然后，將`second`變量的值分配給`first`變量。 最后，將`temp`（其保存`first`）分配給`second`。 這樣就完成了交換過程。 * * * ## 交換數字而不使用臨時變量 ```c #include <stdio.h> int main() { double a, b; printf("Enter a: "); scanf("%lf", &a); printf("Enter b: "); scanf("%lf", &b); // Swapping ? // a = (initial_a - initial_b) a = a - b; ? // b = (initial_a - initial_b) + initial_b = initial_a b = a + b; ? // a = initial_a - (initial_a - initial_b) = initial_b a = b - a; printf("After swapping, a = %.2lf\n", a); printf("After swapping, b = %.2lf", b); return 0; } ``` **輸出** ```c Enter a: 10.25 Enter b: -12.5 After swapping, a = -12.50 After swapping, b = 10.25 ```