# C 程序：将二进制数转换为十进制，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，您将学习通过创建用户定义的函数将二进制数字手动转换为十进制，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)

* * *

## 将二进制转换为十进制的程序

```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;
} 
```

**输出**

```c
Enter a binary number: 110110111
110110111 in binary = 439 
```

* * *

## 将十进制转换为二进制的程序

```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;
} 
```

**输出**

```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 
```