Concatenate one character from string 1 and second character from string 2 - c++

Question

I want to concatenate two strings but it like odd position characters from strin1 and even position characters from stri2.
This is what i have done:
string mainvalue(string og2,string eg2)
{
string odd=og2;
string even=eg2;
string s3;
reverse(odd.begin(),odd.end());
cout<<"Main ordered text is :"<<odd<<endl;
int length1=odd.length();
int length2=even.length();
for(int i=0;i<length1;i++)
{
for(int j=0;j<length2;j++)
{
s3 += odd[j]+even[j];
}
}
cout<<"Complete text is :"<<s3<<endl;
//return s3;
}
Output is look like : :▌π═▌π═▌π═

Answer 1

The reason for your strange output is that you're adding two characters, and adding two alphabetical characters rarely gives a printable result.
But your code would be incorrect even if you could add characters to make strings, as your result would basically be length1 copies of the desired result.
Assuming that the input strings are of equal length, one simple solution is to alternately take one character from each string.
This assumes that the first element is "odd" - if it's "even", just swap the two lines in the loop:
string mainvalue(string odds, string evens)
{
string merged;
for (string::size_type i = 0; i < odds.size(); ++i)
{
merged += odds[i];
merged += evens[i];
}
return merged;
}
You could also do something like this:
string mainvalue(string odds, string evens)
{
auto merged = string {odds.size() + evens.size(), ' '};
auto odd = odds.begin();
auto even = evens.begin();
auto out = merged.begin();
while (odd != odds.end())
{
*out++ = *odd++;
*out++ = *even++;
}
return merged;
}