# C# solution easy to understand mul + sum

• ``````public class Solution {
public string Multiply(string num1, string num2) {
string res="0";
for(int i=num2.Length-1;i>=0;i--)
{
StringBuilder sb=new StringBuilder();
string mul=multiply(num1,num2[i]);
if(mul=="0")
continue;
sb.Append(multiply(num1,num2[i]));
for(int j=0;j<num2.Length-1-i;j++)
{
sb.Append("0");
}
res=plus(res,sb.ToString());
}
return res;
}

public string plus(string s, string t)
{
int m=s.Length-1,n=t.Length-1;
StringBuilder resSb=new StringBuilder();
int caOn=0;
while(m>=0 || n>=0)
{
int sNu=m>-1 ? int.Parse(s[m].ToString()) : 0;
int tNu=n>-1 ? int.Parse(t[n].ToString()) : 0;
int sum = sNu + tNu + caOn;
if(sum>9)
{
sum -= 10;
caOn=1;
}
else
caOn=0;
resSb.Insert(0,sum.ToString());
m--;
n--;
}
if(caOn==1)
resSb.Insert(0,"1");
return resSb.ToString();
}

public string multiply(string s, char chT)
{
string t=chT.ToString();
StringBuilder sb=new StringBuilder();
if(t=="0")
return "0";
int caOn=0;
for(int i=s.Length-1;i>=0;i--)
{
int sum = int.Parse(s[i].ToString())*int.Parse(t)+caOn;
sb.Insert(0,(sum%10).ToString());
caOn = sum/10;
}
if(caOn>0)
sb.Insert(0,caOn.ToString());
return sb.ToString();
}
}``````

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