C++大整数加法解题思路及参考代码

2
1 2
112233445566778899 998877665544332211

3
1111111111111111110

#include<bits/stdc++.h>

using namespace std;

string get_add(string a, string b) {
    int i, add = 0, len = max(a.length(), b.length());
    int nums[1001] = {0};
    reverse(a.begin(), a.end());
    reverse(b.begin(), b.end());
    for(i = 0; i < len; i++) {
        int num1 = (i < a.length()) ? (a[i]-'0') : 0;
        int num2 = (i < b.length()) ? (b[i]-'0') : 0;
        int num = num1 + num2 + add;
        nums[i] = num % 10;
        add = num / 10;
    }

    if(add > 0) // 处理最高位进位
        nums[i] = add;
    string c;
    while(i >= 0) { // 数组逆序拼接得到结果
        c += to_string(nums[i]);
        i--;
    }

    if(c[0] == '0' && c.length() > 1) // 移除前导0
        c.erase(0, 1);
    return c;

}

int main() {
    int T;
    cin >> T;
    string a, b;
    getline(cin, a);
    while(T--) {
        cin >> a >> b;
        string c = get_add(a, b);
        cout << c << endl;
    }
    return 0;
}

#include<string.h>
#include<iostream>

std::string add(std::string s1,std::string s2) {
	std::string s3;
	if(s1.length()<s2.length()) {
		while(s1.length()<s2.length()) {
			s1="0"+s1;
		}
	} else {
		while(s2.length()<s1.length()) {
			s2="0"+s2;
		}
	}
	int up=0;
	int k;
	int len=s1.length()-1;
	while(len>=0) {
		k=(s1.at(len) + s2.at(len) + up - '0' - '0');
		up = k/10;
		s3=(char)(k % 10 + '0') + s3;
		len--;
	}
	if(up)
		s3="1"+s3;
	return s3;
}

std::string sub(std::string s1,std::string s2) {
	if(s1==s2) {
		return "0";
	}
	std::string s3;
	bool flag=false;
	if(s1.length()<s2.length() || (s1.length()==s2.length() && s1<s2)) {
		std::string s=s1;
		s1=s2;
		s2=s;
		flag=true;
	} else {
		s3="";
	}
	while(s2.length()<s1.length()) {
		s2="0" + s2;
	}
	int k,down=0;
	for(int i=s1.length()-1; i>=0; i--) {
		k=s1[i] -s2[i] +down;
		if(k<0) {
			down=-1;
			k=10+k;
		} else {
			down=0;
		}
		s3=(char)('0' + k) + s3;
	}
	k=0;
	while(s3[k]=='0' ) {
		k++;
	}
	s3=s3.substr(k);
	if(flag)
		s3="-"+s3;
	return s3;
}

std::string mul(std::string s1,std::string s2) {
	if(s1=="0" || s2=="0")
		return "0";
	if(s1=="1")
		return s2;
	if(s2=="1")
		return s1;
	std::string s3;
	int len=s1.length() + s2.length() -1;
	for(int i=0; i<len; i++) {
		s3+="0";
	}
	int up=0,k;
	std::string flag="";
	for(int i=s1.length()-1; i>=0; i--) {
		for(int j=s2.length()-1; j>=0; j--) {
			k=s3[i+j]-'0' + (s1[i]-'0')*(s2[j]-'0') ;
			up=k/10;
			s3[i+j]=(char)(k%10+'0');
			int d=1;

			while(up>0) {
				//首位进位
				if(i==0 && j==0 && up>0) {
					flag=(char)("0"+ up);
					break;
				}
				k=(char)(s3[i+j-d]+up-'0');
				up=k/10;
				s3[i+j-d]=(char)(k%10+'0');
				d++;
			}

		}
	}
	return flag + s3;
}