How do I get the sum of two strings that are numbers? For example:
string num1 = "12"; string num2 = "4"; string sum = num1 + num2; So string sum will equal "16"
How do I do this in c++?
I tried doing it with ascii characters but it does not work I cannot convert the string to an integer as well
To add large integers using string, you can do something like this.
string doSum(string a, string b) { if(a.size() < b.size()) swap(a, b); int j = a.size()-1; for(int i=b.size()-1; i>=0; i--, j--) a[j]+=(b[i]-'0'); for(int i=a.size()-1; i>0; i--) { if(a[i] > '9') { int d = a[i]-'0'; a[i-1] = ((a[i-1]-'0') + d/10) + '0'; a[i] = (d%10)+'0'; } } if(a[0] > '9') { string k; k+=a[0]; a[0] = ((a[0]-'0')%10)+'0'; k[0] = ((k[0]-'0')/10)+'0'; a = k+a; } return a; } int main() { string result = doSum("1234567890", "123789456123"); cout << result << "\n"; } Output
125024024013 Reference: See the complete code at Ideone.com
string sum = ... isn't the same as cout << sum << "\n";!
dim sum.
The flat answer is
string sum = std::to_string(std::stoi(num1) + std::stoi(num2)); See the Live Demo.
The broader answer as for your comment is:
You cannot use that technique to do math with big integer values.
That requires using an appropriate 3rd party library.
The answer to your question can be written like this
string addStrings(string num1, string num2) { string res=""; int n=num1.size(); int m=num2.size(); int carry=0; int j; for(int i=n-1,j=m-1;i>=0 || j>=0;i--, j--){ int a; if(i>=0){ a=((int)(num1[i])-48); } else { a=0; } int b; if(j>=0){ b=((int)(num2[j])-48); } else{ b=0; } cout<<num1[i]<<" "<<num2[i]<<endl; cout<<a<<" "<<b<<endl; int sum=carry+a+b; int u=sum%10; res+=u; carry=sum/10; } res+=carry; cout<<res<<endl; reverse(res.begin(),res.end()); return res; } I added cout statements to check what's going on inside the function