[C++知识库]C++ 进制转换 & 二进制运算

#include<bits/stdc++.h>
using namespace std;

//10进制转为目标进制
void show(int num, int target) {
  string ans = "";
  if(num == 0) {cout<<"0"; return;}
  while(num) {
    int tmp = num % target;
    if(tmp >= 0 && tmp <= 9)
      ans += tmp+'0';
    else 
      ans += tmp-10+'a';
    num /= target;
  }
  reverse(ans.begin(), ans.end());
  cout<<ans<<endl;
  return;
}

//加法
int add(int a, int b) {
  int res = a;
  while(b) {
    int tmp = a;
    a = a ^ b;
    b = (tmp & b)<<1;
    res = a;
  }
  return res;
}
//减法
int subtraction(int a, int b) {
  b = add(~b, 1); //取相反数
  int res = add(a, b);
  return res;
}

//乘法
int mul(int a, int b) {
  bool isNeg = false;
  if((a<0 && b>0) || (a>0 && b<0)) {
    isNeg = true;
  }
  if(a < 0) a = add(~a,1);//求出a的绝对值
  if(b < 0) b = add(~b,1);//求出b的绝对值
  
  int res = 0;
  while(b) {
    //当前位 为b的最右边一位
    if(b & 1) {
      res = add(res, a);
    }
    a = a<<1;
    b = b>>1;
  }
  if(isNeg) {
    res = add(~res, 1);
  }
  return res;
}

//除法
int divide(int a, int b) {
  if(b==0) throw std::runtime_error("Divided can't be zero...");

  bool isNeg = false;
  if((a<0 && b>0) || (a>0 && b<0)) {
    isNeg = true;
  }
  if(a < 0) a = add(~a,1);//求出a的绝对值
  if(b < 0) b = add(~b,1);//求出b的绝对值

  int res = 0;
  while(a >= b) {
    res = add(res, 1);
    a = subtraction(a,b);
  }
  if(isNeg)
    res = add(~res, 1);
  return res;
}

int main() {
  int a = 10, b = 0;
  cout<<"a + b = "<<add(a, b)<<endl;
  cout<<"a - b = "<<subtraction(a, b)<<endl;
  cout<<"a * b = "<<mul(a,b)<<endl;
  cout<<"a / b = "<<divide(a,b)<<endl;
  return 0;
}

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