# Easy understand C++

• ``````class Solution {
//大数相乘 and 大数相加
public:
string multiply(string num1, string num2) {
int len1 = num1.size();
int len2 = num2.size();
string res = "";
for(int i = len1 - 1; i>=0;i--)
{
string s = "";
int sum = 0;
for(int j = len2 - 1; j>=0;j--)
{
int temp = 0;
sum += (num2[j] - '0') * (num1[i] - '0');
temp = sum%10;
sum /= 10;
s += (temp + '0');
}
if(sum != 0) s += (sum + '0');
for(int k = 0;k<len1-1-i;k++)
{
s = '0' + s;
}
}
reverse(res.begin(),res.end());
int i = 0;
for(i;i < res.size() ; i++)
{
if(res[i] != '0') break;
}
return i==res.size()?"0":res;
}
{
int len1 = res.size() - 1;
int len2 = s.size() - 1;
reverse(res.begin(),res.end());
reverse(s.begin(),s.end());
int sum = 0;
string k = "";
while(len1 >= 0 || len2 >= 0 || sum>0)
{
if(len1 >= 0)
{
sum += (res[len1--] - '0');
}
if(len2 >= 0)
{
sum += (s[len2--] - '0');
}
k += (sum%10 + '0');
sum /= 10;
}
return k;
}
};
···``````

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