# C 程序：将八进制数转换为十进制，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，您将学习通过创建用户定义的函数将八进制数手动转换为十进制，反之亦然。

要理解此示例，您应该了解以下 [C 编程](/c-programming "C tutorial")主题：

*   [C 函数](/c-programming/c-functions)
*   [C 用户定义的函数](/c-programming/c-user-defined-functions)

* * *

## 示例 1：将十进制转换为八进制的程序

```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;
} 
```

**输出**

```c
Enter a decimal number: 78
78 in decimal = 116 in octal
```

## 示例 2：将八进制转换为十进制的程序

```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;
} 
```

**输出**

```c
Enter an octal number: 116
116 in octal = 78 in decimal 
```