题目：进制转换合集。任意r进制与十进制之间的转换

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<ctype.h>
long stringToDecimal(const char* str, int base);
void convertToBaseR(int num, int r);

int main() {
	char hexStr[] = "1A3F";
	char octStr[] = "123";
	char binStr[] = "101010";
	printf("十六进制转换成十进制为: %ld\n", stringToDecimal(hexStr, 16));
	printf("八进制转换成十进制为: %ld\n", stringToDecimal(octStr, 8));
	printf("二进制转换成十进制为: %ld\n", stringToDecimal(binStr, 2));

	int num, r;
	printf("请输入十进制的整数: ");
	scanf_s("%d", &num);
	printf("请输入要转化的进制数: ");
	scanf_s("%d", &r);
	convertToBaseR(num, r);

	return 0;
}

/// <summary>
/// 将字符串str转为十进制
/// </summary>
/// <param name="str">字符串</param>
/// <param name="base">基数2， 8， 16等</param>
/// <returns></returns>
long stringToDecimal(const char* str, int base) {
	long result = 0;
	int multiplier = 1;
	int length = strlen(str);

	//从字符串末尾开始解析
	for (int  i = length - 1; i >= 0; i--)
	{
		char ch = tolower(str[i]);
		int digit = -1;

		//根据字符计算其对应的值
		if (ch >= '0' && ch <= '9') 
		{
			digit = ch - '0';//将字符串转换成对应的数字
		}
		else if(base == 16 && (ch >= 'a' && ch <= 'f'))
		{
			digit = ch - 'a' + 10;
		}
		else if(ch < '0' || (ch > '9' && base !=16) ||(base == 16) && ch > 'f')
		{
			//出错
			return 0;
		}

		//判断是否在有效范围内
		if (digit >= base) {
			return 0;
		}

		result += digit * multiplier;  //更新累加结果

		multiplier *= base;//更新下一次计算的基数
	}

}



/// <summary>
/// 将十进制数转换成任意的r进制数
/// </summary>
/// <param name="num">数字</param>
/// <param name="r">要转换的目标进制数</param>
void convertToBaseR(int num, int r) {
	int index = 0;
	char result[65];//假设转换后的数不超过64位

	//处理num = 0的情况
	if (num == 0) {
		printf("0\n");
		return;
	}

	while (num > 0)
	{
		int remainder = num % r;
		if (remainder < 10) {
			result[index++] = '0' + remainder;//余数小于10的,将其转换成0~9之间的字符
		}
		else
		{
			result[index++] = 'A' + (remainder - 10);//余数大于10的，将其转换成'A' ~ 'Z' 字符
		}

		num = num / r; //更新下一次参与计算的数字
	}

	result[index] = '\0'; //在字符串末尾添加结束符

	//因为结果是从低位到高位存储的，所以需要反向打印
	for (int i = index; i >= 0; i--)
	{
		printf("%c", result[i]);
	}
	printf("\n");
}