# C 程序：將八進制數轉換為十進制，反之亦然 > 原文： [https://www.programiz.com/c-programming/examples/octal-decimal-convert](https://www.programiz.com/c-programming/examples/octal-decimal-convert) #### 在此示例中，您將學習通過創建用戶定義的函數將八進制數手動轉換為十進制，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) * * * ## 示例 1：將十進制轉換為八進制的程序 ```c #include <stdio.h> #include <math.h> int convertDecimalToOctal(int decimalNumber); int main() { int decimalNumber; printf("Enter a decimal number: "); scanf("%d", &decimalNumber); printf("%d in decimal = %d in octal", decimalNumber, convertDecimalToOctal(decimalNumber)); return 0; } int convertDecimalToOctal(int decimalNumber) { int octalNumber = 0, i = 1; while (decimalNumber != 0) { octalNumber += (decimalNumber % 8) * i; decimalNumber /= 8; i *= 10; } return octalNumber; } ``` **輸出** ```c Enter a decimal number: 78 78 in decimal = 116 in octal ``` ## 示例 2：將八進制轉換為十進制的程序 ```c #include <stdio.h> #include <math.h> long long convertOctalToDecimal(int octalNumber); int main() { int octalNumber; printf("Enter an octal number: "); scanf("%d", &octalNumber); printf("%d in octal = %lld in decimal", octalNumber, convertOctalToDecimal(octalNumber)); return 0; } long long convertOctalToDecimal(int octalNumber) { int decimalNumber = 0, i = 0; while(octalNumber != 0) { decimalNumber += (octalNumber%10) * pow(8,i); ++i; octalNumber/=10; } i = 1; return decimalNumber; } ``` **輸出** ```c Enter an octal number: 116 116 in octal = 78 in decimal ```