# C 程序：將二進制數轉換為十進制，反之亦然 > 原文： [https://www.programiz.com/c-programming/examples/binary-decimal-convert](https://www.programiz.com/c-programming/examples/binary-decimal-convert) #### 在此示例中，您將學習通過創建用戶定義的函數將二進制數字手動轉換為十進制，反之亦然。 要理解此示例，您應該了解以下 [C 編程](/c-programming "C tutorial")主題： * [C 函數](/c-programming/c-functions) * [C 用戶定義的函數](/c-programming/c-user-defined-functions) * * * ## 將二進制轉換為十進制的程序 ```c #include <math.h> #include <stdio.h> int convert(long long n); int main() { long long n; printf("Enter a binary number: "); scanf("%lld", &n); printf("%lld in binary = %d in decimal", n, convert(n)); return 0; } int convert(long long n) { int dec = 0, i = 0, rem; while (n != 0) { rem = n % 10; n /= 10; dec += rem * pow(2, i); ++i; } return dec; } ``` **輸出** ```c Enter a binary number: 110110111 110110111 in binary = 439 ``` * * * ## 將十進制轉換為二進制的程序 ```c #include <math.h> #include <stdio.h> long long convert(int n); int main() { int n; printf("Enter a decimal number: "); scanf("%d", &n); printf("%d in decimal = %lld in binary", n, convert(n)); return 0; } long long convert(int n) { long long bin = 0; int rem, i = 1, step = 1; while (n != 0) { rem = n % 2; printf("Step %d: %d/2, Remainder = %d, Quotient = %d\n", step++, n, rem, n / 2); n /= 2; bin += rem * i; i *= 10; } return bin; } ``` **輸出** ```c Enter a decimal number: 19 Step 1: 19/2, Remainder = 1, Quotient = 9 Step 2: 9/2, Remainder = 1, Quotient = 4 Step 3: 4/2, Remainder = 0, Quotient = 2 Step 4: 2/2, Remainder = 0, Quotient = 1 Step 5: 1/2, Remainder = 1, Quotient = 0 19 in decimal = 10011 in binary ```