From submitter Christoph comes a function that makes your average regex seem not all that bad, actually:

According to "What is a Titration?" we learn that "a titration is a technique where a solution of known concentration is used to determine the concentration of an unknown solution." Since this is an often needed calculation in a laboratory, we can write a program to solve this problem for us.

Part of the solver is a formula parser, which needs to accept variable names (either lower or upper case letters), decimal numbers, and any of '+-*/^()' for mathematical operators. Presented here is the part of the code for the solveTitration() function that deals with parsing of the formula. Try to read it in an 80 chars/line window. Once with wrapping enabled, and once with wrapping disabled and horizontal scrolling. Enjoy!
String solveTitration(char *yvalue)
{
    String mreport;
    lettere = 0;
    //now we have to solve the system of equations
    //yvalue contains the equation of Y-axis variable
    String tempy = "";
    end = 1;
    mreport = "";
    String tempyval;
    String ptem;
    for (int i = 0; strlen(yvalue) + 1; ++i) {
        if (!(yvalue[i]=='q' || yvalue[i]=='w' || yvalue[i]=='e' 
|| yvalue[i]=='r' || yvalue[i]=='t' || yvalue[i]=='y' || yvalue[i]=='u' || 
yvalue[i]=='i' || yvalue[i]=='o' || yvalue[i]=='p' || yvalue[i]=='a' || 
yvalue[i]=='s' || yvalue[i]=='d' || yvalue[i]=='f' || yvalue[i]=='g' || 
yvalue[i]=='h' || yvalue[i]=='j' || yvalue[i]=='k' || yvalue[i]=='l' || 
yvalue[i]=='z' || yvalue[i]=='x' || yvalue[i]=='c' || yvalue[i]=='v' || 
yvalue[i]=='b' || yvalue[i]=='n' || yvalue[i]=='m' || yvalue[i]=='+' || 
yvalue[i]=='-' || yvalue[i]=='^' || yvalue[i]=='*' || yvalue[i]=='/' || 
yvalue[i]=='(' || yvalue[i]==')' || yvalue[i]=='Q' || yvalue[i]=='W' || 
yvalue[i]=='E' || yvalue[i]=='R' || yvalue[i]=='T' || yvalue[i]=='Y' || 
yvalue[i]=='U' || yvalue[i]=='I' || yvalue[i]=='O' || yvalue[i]=='P' || 
yvalue[i]=='A' || yvalue[i]=='S' || yvalue[i]=='D' || yvalue[i]=='F' || 
yvalue[i]=='G' || yvalue[i]=='H' || yvalue[i]=='J' || yvalue[i]=='K' || 
yvalue[i]=='L' || yvalue[i]=='Z' || yvalue[i]=='X' || yvalue[i]=='C' || 
yvalue[i]=='V' || yvalue[i]=='B' || yvalue[i]=='N' || yvalue[i]=='M' || 
yvalue[i]=='1' || yvalue[i]=='2' || yvalue[i]=='3' || yvalue[i]=='4' || 
yvalue[i]=='5' || yvalue[i]=='6' || yvalue[i]=='7' || yvalue[i]=='8' || 
yvalue[i]=='9' || yvalue[i]=='0' || yvalue[i]=='.' || yvalue[i]==',')) {
            break; //if current value is not a permitted value, this means that something is wrong
        }
        if (yvalue[i]=='q' || yvalue[i]=='w' || yvalue[i]=='e' 
|| yvalue[i]=='r' || yvalue[i]=='t' || yvalue[i]=='y' || yvalue[i]=='u' || 
yvalue[i]=='i' || yvalue[i]=='o' || yvalue[i]=='p' || yvalue[i]=='a' || 
yvalue[i]=='s' || yvalue[i]=='d' || yvalue[i]=='f' || yvalue[i]=='g' || 
yvalue[i]=='h' || yvalue[i]=='j' || yvalue[i]=='k' || yvalue[i]=='l' || 
yvalue[i]=='z' || yvalue[i]=='x' || yvalue[i]=='c' || yvalue[i]=='v' || 
yvalue[i]=='b' || yvalue[i]=='n' || yvalue[i]=='m' || yvalue[i]=='Q' || 
yvalue[i]=='W' || yvalue[i]=='E' || yvalue[i]=='R' || yvalue[i]=='T' || 
yvalue[i]=='Y' || yvalue[i]=='U' || yvalue[i]=='I' || yvalue[i]=='O' || 
yvalue[i]=='P' || yvalue[i]=='A' || yvalue[i]=='S' || yvalue[i]=='D' || 
yvalue[i]=='F' || yvalue[i]=='G' || yvalue[i]=='H' || yvalue[i]=='J' || 
yvalue[i]=='K' || yvalue[i]=='L' || yvalue[i]=='Z' || yvalue[i]=='X' || 
yvalue[i]=='C' || yvalue[i]=='V' || yvalue[i]=='B' || yvalue[i]=='N' || 
yvalue[i]=='M' || yvalue[i]=='.' || yvalue[i]==',') {
            lettere = 1; //if lettere == 0 then the equation contains only mnumbers
        }
        if (yvalue[i]=='+' || yvalue[i]=='-' || yvalue[i]=='^' || 
yvalue[i]=='*' || yvalue[i]=='/' || yvalue[i]=='(' || yvalue[i]==')' || 
yvalue[i]=='1' || yvalue[i]=='2' || yvalue[i]=='3' || yvalue[i]=='4' || 
yvalue[i]=='5' || yvalue[i]=='6' || yvalue[i]=='7' || yvalue[i]=='8' || 
yvalue[i]=='9' || yvalue[i]=='0' || yvalue[i]=='.' || yvalue[i]==',') {
            tempyval = tempyval + String(yvalue[i]);
        } else {
            tempy = tempy + String(yvalue[i]);
            for (int i = 0; i < uid.tableWidget->rowCount(); ++i) {
                TableItem *titem = uid.table->item(i, 0);
                TableItem *titemo = uid.table->item(i, 1);
                if (!titem || titem->text().isEmpty()) {
                    break;
                } else {
                    if (tempy == uid.xaxis->text()) {
                        tempyval = uid.xaxis->text();
                        tempy = "";
                    }
                    ... /* some code omitted here */
                    if (tempy!=uid.xaxis->text()) {
                        if (yvalue[i]=='+' || yvalue[i]=='-' 
|| yvalue[i]=='^' || yvalue[i]=='*' || yvalue[i]=='/' || yvalue[i]=='(' || 
yvalue[i]==')' || yvalue[i]=='1' || yvalue[i]=='2' || yvalue[i]=='3' || 
yvalue[i]=='4' || yvalue[i]=='5' || yvalue[i]=='6' || yvalue[i]=='7' || 
yvalue[i]=='8' || yvalue[i]=='9' || yvalue[i]=='0' || yvalue[i]=='.' || 
yvalue[i]==',') {
                            //actually nothing
                        } else {
                            end = 0;
                        }
                    }
                }
            }
        } // simbol end
        if (!tempyval.isEmpty()) {
            mreport = mreport + tempyval;
        }
        tempyval = "";
    }
    return mreport;
}
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