def convert_base(num, from_base, to_base):
    # 将输入数从原始进制转换为十进制
    decimal_num = int(str(num), from_base)
    
    # 将十进制数转换为目标进制
    if decimal_num == 0:
        return '0'
    
    digits = []
    while decimal_num > 0:
        remainder = decimal_num % to_base
        if remainder >= 10:
            digits.append(chr(ord('A') + remainder - 10))
        else:
            digits.append(str(remainder))
        decimal_num //= to_base
    
    # 反转数字列表并连接成字符串
    result = ''.join(digits[::-1])
    return result

# 示例：将二进制数1011转换为十六进制数
num = "1011"
from_base = 2
to_base = 16
converted_num = convert_base(num, from_base, to_base)
print(converted_num)  # 输出结果为B