Language: C++

#include<bits/stdc++.h> 
using namespace std; 
#define ll long long int
  
// Multiplies str1 and str2, and prints result. 
string multiply(string num1, string num2) 
{ 
    int len1 = num1.size(); 
    int len2 = num2.size(); 
    if (len1 == 0 || len2 == 0) 
    return "0"; 
  
    // will keep the result number in vector 
    // in reverse order 
    vector<int> result(len1 + len2, 0); 
  
    // Below two indexes are used to find positions 
    // in result.  
    int i_n1 = 0;  
    int i_n2 = 0;  
      
    // Go from right to left in num1 
    for (int i=len1-1; i>=0; i--) 
    { 
        int carry = 0; 
        int n1 = num1[i] - '0'; 
  
        // To shift position to left after every 
        // multiplication of a digit in num2 
        i_n2 = 0;  
          
        // Go from right to left in num2              
        for (int j=len2-1; j>=0; j--) 
        { 
            // Take current digit of second number 
            int n2 = num2[j] - '0'; 
  
            // Multiply with current digit of first number 
            // and add result to previously stored result 
            // at current position.  
            int sum = n1*n2 + result[i_n1 + i_n2] + carry; 
  
            // Carry for next iteration 
            carry = sum/10; 
  
            // Store result 
            result[i_n1 + i_n2] = sum % 10; 
  
            i_n2++; 
        } 
  
        // store carry in next cell 
        if (carry > 0) 
            result[i_n1 + i_n2] += carry; 
  
        // To shift position to left after every 
        // multiplication of a digit in num1. 
        i_n1++; 
    } 
  
    // ignore '0's from the right 
    int i = result.size() - 1; 
    while (i>=0 && result[i] == 0) 
    i--; 
  
    // If all were '0's - means either both or 
    // one of num1 or num2 were '0' 
    if (i == -1) 
    return "0"; 
  
    // generate the result string 
    string s = ""; 
      
    while (i >= 0) 
        s += std::to_string(result[i--]); 
  
    return s; 
} 
  
// Driver code 
int main() 
{ 
    string str1,str2;
    cin>>str1;
    string str3;cin>>str3;
   str2="";
    for(ll i=0;i<str3.size();i++){if(str3[i]!='.') str2=str2+str3[i];}
    if(str1=='0'||str2=='0') {cour<<"0";return 0;}
    
    
      
    if((str1.at(0) == '-' || str2.at(0) == '-') &&  
        (str1.at(0) != '-' || str2.at(0) != '-' )) 
        cout<<"-"; 
  
  
    if(str1.at(0) == '-' && str2.at(0)!='-') 
        { 
            str1 = str1.substr(1); 
        } 
        else if(str1.at(0) != '-' && str2.at(0) == '-') 
        { 
            str2 = str2.substr(1); 
        } 
        else if(str1.at(0) == '-' && str2.at(0) == '-') 
        { 
            str1 = str1.substr(1); 
            str2 = str2.substr(1); 
        } 
       
    if(str2[0]=='0'&&str2[1]=='0'){str2=str2[2];
string s4=multiply(str1,str2);
string s5="00";
 s5=s5+s4;
for(long long int i=0;i<s5.size()-2;i++) cout<<s5[i];return 0;
return 0;
    }
  string s3=multiply(str1, str2);
    for(long long int i=0;i<s3.size()-2;i++) cout<<s3[i];
    return 0; 
}

Compiler output:
a.cc: In function 'int main()':
a.cc:88:12: error: no match for 'operator==' (operand types are 'std::string' {aka 'std::__cxx11::basic_string<char>'} and 'char')
   88 |     if(str1=='0'||str2=='0') {cour<<"0";return 0;}
      |        ~~~~^~~~~
      |        |     |
      |        |     char
      |        std::string {aka std::__cxx11::basic_string<char>}
In file included from /usr/include/c++/14/regex:68,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:181,
                 from a.cc:1:
/usr/include/c++/14/bits/regex.h:1103:5: note: candidate: 'template<class _BiIter> bool std::__cxx11::operator==(const sub_match<_BiIter>&, const sub_match<_BiIter>&)'
 1103 |     operator==(const sub_match<_BiIter>& __lhs, const sub_match<_BiIter>& __rhs)
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1103:5: note:   template argument deduction/substitution failed:
a.cc:88:14: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   88 |     if(str1=='0'||str2=='0') {cour<<"0";return 0;}
      |              ^~~
/usr/include/c++/14/bits/regex.h:1199:5: note: candidate: 'template<class _Bi_iter, class _Ch_traits, class _Ch_alloc> bool std::__cxx11::operator==(__sub_match_string<_Bi_iter, _Ch_traits, _Ch_alloc>&, const sub_match<_BiIter>&)'
 1199 |     operator==(const __sub_match_string<_Bi_iter, _Ch_traits, _Ch_alloc>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1199:5: note:   template argument deduction/substitution failed:
a.cc:88:14: note:   mismatched types 'const std::__cxx11::sub_match<_BiIter>' and 'char'
   88 |     if(str1=='0'||str2=='0') {cour<<"0";return 0;}
      |              ^~~
/usr/include/c++/14/bits/regex.h:1274:5: note: candidate: 'template<class _Bi_iter, class _Ch_traits, class _Ch_alloc> bool std::__cxx11::operator==(const sub_match<_BiIter>&, __sub_match_string<_Bi_iter, _Ch_traits, _Ch_alloc>&)'
 1274 |     operator==(const sub_match<_Bi_iter>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1274:5: note:   template argument deduction/substitution failed:
a.cc:88:14: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   88 |     if(str1=='0'||str2=='0') {cour<<"0";return 0;}
      |              ^~~
/usr/include/c++/14/bits/regex.h:1366:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator==(const typename std::iterator_traits<_Iter>::value_type*, const sub_match<_BiIter>&)'
 1366 |     operator==(typename iterator_traits<_Bi_iter>::value_type const* __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1366:5: note:   template argument deduction/substitution failed:
a.cc:88:14: note:   mismatched types 'const std::__cxx11::sub_match<_BiIter>' and 'char'
   88 |     if(str1=='0'||str2=='0') {cour<<"0";return 0;}
      |              ^~~
/usr/include/c++/14/bits/regex.h:1441:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator==(const sub_match<_BiIter>&, const typename std::iterator_traits<_Iter>::value_type*)'
 1441 |     operator==(const sub_match<_Bi_iter>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1441:5: note:   template argument deduction/substitution failed:
a.cc:88:14: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   88 |     if(str1=='0'||str2=='0') {cour<<"0";return 0;}
      |              ^~~
/usr/include/c++/14/bits/regex.h:1534:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator==(const typename std::iterator_traits<_Iter>::value_type&, const sub_match<_BiIter>&)'
 1534 |     operator==(typename iterator_traits<_Bi_iter>::value_type const& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1534:5: note:   template argument deduction/substitution failed:
a.cc:88:14: note:   mismatched types 'const std::__cxx11::sub_match<_BiIter>' and 'char'
   88 |     if(str1=='0'||str2=='0') {cour<<"0";return 0;}
      |              ^~~
/usr/include/c++/14/bits/regex.h:1613:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator==(const sub_match<_BiIter>&, const typename std::iterator_traits<_Iter>::value_type&)'
 1613 |     operator==(const sub_match<_Bi_iter>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1613:5: note:   template argument deduction/substitution failed:
a.cc:88:14: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   88 |     if(str1=='0'||str2=='0') {cour<<"0";return 0;}
      |              ^~~
/usr/include/c++/14/bits/regex.h:2186:5: note: candidate: 'template<class _Bi_iter, class _Alloc> bool std::__cxx11::operator==(const match_results<_BiIter, _Alloc>&, const match_results<_BiIter, _Alloc>&)'
 2186 |     operator==(const match_results<_Bi_iter, _Alloc>& __m1,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:2186:5: note:   template argument deduction/substitution failed:
a.cc:88:14: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::__cxx11::match_results<_BiIter, _Alloc>'
   88 |     if(str1=='0'||str2=='0') {cour<<"0";return 0;}
      |              ^~~
In file included from /usr/include/c++/14/bits/stl_algobase.h:64,
                 from /usr/include/c++/14/algorithm:60,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:51:
/usr/include/c++/14/bits/stl_pair.h:1033:5: note: candidate: 'template<class _T1, class _T2> constexpr bool std::operator==(const pair<_T1, _T2>&, const pair<_T1, _T2>&)'
 1033 |     operator==(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_pair.h:1033:5: note:   template argument deduction/substitution failed:
a.cc:88:14: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::pair<_T1, _T2>'
   88 |     if(str1=='0'||str2=='0') {cour<<"0";return 0;}
      |              ^~~
In file included from /usr/include/c++/14/bits/stl_algobase.h:67:
/usr/include/c++/14/bits/stl_iterator.h:441:5: note: candidate: 'template<class _Iterator> constexpr bool std::operator==(const reverse_iterator<_Iterator>&, const reverse_iterator<_Iterator>&)'
  441 |     operator==(const reverse_iterator<_Iterator>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:441:5: note:   template argument deduction/substitution failed:
a.cc:88:14: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::reverse_iterator<_Iterator>'
   88 |     if(str1=='0'||str2=='0') {cour<<"0";return 0;}
      |              ^~~
/usr/include/c++/14/bits/stl_iterator.h:486:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr bool std::operator==(const reverse_iterator<_Iterator>&, const reverse_iterator<_IteratorR>&)'
  486 |     operator==(const reverse_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:486:5: note:   template argument deduction/substitution failed:
a.cc:88:14: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::reverse_iterator<_Iterator>'
   88 |     if(str1=='0'||str2=='0') {cour<<"0";return 0;}
      |              ^~~
/usr/include/c++/14/bits/stl_iterator.h:1667:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr bool std::operator==(const move_iterator<_IteratorL>&, const move_iterator<_IteratorR>&)'
 1667 |     operator==(const move_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1667:5: note:   template argument deduction/substitution failed:
a.cc:88:14: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::move_iterator<_IteratorL>'
   88 |     if(str1=='0'||str2=='0') {cour<<"0";return 0;}
      |              ^~~
/usr/include/c++/14/bits/stl_iterator.h:1737:5: note: candidate: 'template<class _Iterator> constexpr bool std::operator==(const move_iterator<_IteratorL>&, const move_iterator<_IteratorL>&)'
 1737 |     operator==(const move_iterator<_Iterator>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1737:5: note:   template argument deduction/substitution failed:
a.cc:88:14: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::move_iterator<_IteratorL>'
   88 |     if(str1=='0'||str2=='0') {cour<<"0";return 0;}
      |              ^~~
In file included from /usr/include/c++/14/bits/char_traits.h:42,
                 from /usr/include/c++/14/string:42,
                 from /usr/include/c++/14/bitset:52,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:52:
/usr/include/c++/14/bits/postypes.h:192:5: note: candidate: 'template<class _StateT> bool std::operator==(const fpos<_StateT>&, const fpos<_StateT>&)'
  192 |     operator==(const fpos<_StateT>& __lhs, const fpos<_StateT>& __rhs)
      |     ^~~~~~~~
/usr/include/c++/14/bits/postypes.h:192:5: note:   template argument deduction/substitution failed:
a.cc:88:14: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::fpos<_StateT>'
   88 |     if(str1=='0'||str2=='0') {cour<<"0";return 0;}
      |              ^~~
In file included from /usr/include/c++/14/string:43:
/usr/include/c++/14/bits/allocator.h:235:5: note: candidate: 'template<class _T1, class _T2> bool std::operator==(const allocator<_CharT>&, const allocator<_T2>&)'
  235 |     operator==(const allocator<_T1>&, const allocator<_T2>&)
      |     ^~~~~~~~
/usr/include/c++/14/bits/allocator.h:235:5: note:   template argument deduction/substitution failed:
a.cc:88:14: note:   'std::string' {aka 'std::__cxx11::basic_string<char>'} is not derived from 'const std::allocator<_CharT>'
   88 |     if(str1=='0'||str2=='0') {cour<<"0";return 0;}
      |              ^~~
In file included from /usr/include/c++/14/bits/basic_string.h:47,
                 from /usr/include/c++/14/string:54:
/usr/include/c++/14/string_view:629:5: note: candidate: 'template<class _CharT, class _Traits>