#include <stdio.h>
int main()
{
    int x, n;
    scanf("%d %d", &x, &n);//x是要轉(zhuǎn)換的十進制數(shù)，n為要轉(zhuǎn)換成的進制
    int arr[100] = { 0 };//創(chuàng)建一個足夠大的數(shù)組來存放余數(shù)
    int i = 0,j = 0;
    while (x)
    {
        arr[i++] = x % n;//存放余數(shù)，i最后的值正好是余數(shù)的個數(shù)
        x /= n;
    }
    for (j = i - 1; j >= 0; j--)
    {
        printf("%d", arr[j]);//余數(shù)倒序輸出
    }
    printf("\n");
    return 0;
}

#include <stdio.h>
int main()
{
    int x;
    scanf("%d", &x);
    char arr[100] = { 0 };//因為十六進制中會出現(xiàn)A\B\C\D\E\F等字符，所以保存余數(shù)的數(shù)組類型應定義為char
    int i = 0, j = 0;
    while (x)
    {
        arr[i++] = x % 16;
        x /= 16;
    }
    for (j = 0; j < i; j++)
    {
        //將取出的余數(shù)轉(zhuǎn)換為對應的字符
        switch (arr[j])
        {
        case 10:arr[j] = 'A'; break;
        case 11:arr[j] = 'B'; break;
        case 12:arr[j] = 'C'; break;
        case 13:arr[j] = 'D'; break;
        case 14:arr[j] = 'E'; break;
        case 15:arr[j] = 'F'; break;
        default:arr[j] += 48;
        }
    }
    for (j = i - 1; j >= 0; j--)
    {
        printf("%c", arr[j]);//逆序打印
    }
    printf("\n");
    return 0;
}

#include <stdio.h>
#include <math.h>
int main()
{
    int n = 0, sum = 0, i = 0, x = 0;
    scanf("%d %d", &x, &n);//x為輸入的二進制或八進制的數(shù)，n為進制。
    while (x)
    {
        sum += (x%10)*pow(n, i++);//x%10將x的每一位取出，再與這個位上的權重相乘。
        x /= 10;
    }
    printf("%d\n", sum);
    return 0;
}

#include <stdio.h>
#include <string.h>
#include <math.h>
int main()
{
    char arr1[100] = { 0 };
    scanf("%s", arr1);
    int len = strlen(arr1);
    int i = 0,  sum = 0;
    for (i = 0; i<len; i++)
    {
        int temp = 0;
        switch (arr1[i])
        {
        case 'A':temp = 10; break;
        case 'B':temp = 11; break;
        case 'C':temp = 12; break;
        case 'D':temp = 13; break;
        case 'E':temp = 14; break;
        case 'F':temp = 15; break;
        default:temp = arr1[i] - '0'; break;
        //將各個位上的字符轉(zhuǎn)換為對應的數(shù)字
        }
        sum += temp * pow(16, len-i-1);//各個位上的權重相乘再相加
    }
    printf("%d\n", sum);
    return 0;
}