Macro Replacement during Code Generation

for(each line in the program)
{
    for(each macro definition)
    {
        test if the macro appears;
        perform replacement if needed;
    }
}

for(each line in the program)
{
    tokenize the line;
    for(each token in the line)
    {
        switch(based on the token type)
        {
            case(an identifier)
                lookup the identifier in the table of macro names;
                perform replacement as necessary;
            ....
        }
    }
}

int c = a + b