Question

The operator ++ should be equivalent to + 1, so why does the following example produce different results?

#include <iostream>
#include <string>

int main()
{
    int i, n=25;
    std::string s1="a", s2="a", s1p="", s2p="";

    for (i=0;i<=n;i++)
    {
        s1p += s1;
        s1 = s1.at(0) + 1;

        s2p += s2;
        s2 = s2.at(0)++;
    }
    std::cout << "s1p = " << s1p << "\n" << "s2p = " << s2p << "\n";

    return 0;
}

Ouput:
s1p = abcdefghijklmnopqrstuvwxyz
s2p = aaaaaaaaaaaaaaaaaaaaaaaaaa

Answer 1

The post-increment returns the value previously held by the variable.

Think of x++ (post-increment) as

int y = x;
x = x+1;
return y;

and of ++x (pre-increment) as

x = x+1;
return x;

To achieve your desired result, you need pre-increment.