You are assigning ASCII value of 6 to the last character of string. Please refer to ASCII chart online. To simply answer your question, you can add '0' to ur last_dig. That should work.

 myStr[myStr_sz-1] = last_dig + '0'; 

But why are u doing like this? What if the last digit is 9? When u add 1, you will need to add the second last digit as well. A better solution would be to completely convert the string to digit, do the arithmetric operation, and then convert it back to QString

@Swati777999 said in Operations with QString and int:

You are assigning ASCII value of 6 to the last character of string. Please refer to ASCII chart online. To simply answer your question, you can add '0' to ur last_dig. That should work.

 myStr[myStr_sz-1] = last_dig + '0'; 

But why are u doing like this? What if the last digit is 9? When u add 1, you will need to add the second last digit as well. A better solution would be to completely convert the string to digit, do the arithmetric operation, and then convert it back to QString

Here's my try with real values

  QString myStr = "99.20";
    qDebug()<<"old String is =" <<myStr;
    int indx = myStr.indexOf(".");
    myStr.remove('.');
    float myStr_int = myStr.toFloat();   //100  
    myStr_int +=1;
    QString myStrNew = QString::number(myStr_int);
    myStrNew.insert(indx,".");
    qDebug()<<"New int value is =" <<myStrNew.toFloat();

@Swati777999 said in Operations with QString and int:

You are assigning ASCII value of 6 to the last character of string. Please refer to ASCII chart online. To simply answer your question, you can add '0' to ur last_dig. That should work.

 myStr[myStr_sz-1] = last_dig + '0'; 

But why are u doing like this? What if the last digit is 9? When u add 1, you will need to add the second last digit as well. A better solution would be to completely convert the string to digit, do the arithmetric operation, and then convert it back to QString

Yes, your suggestion works perfectly well.

    QString myStr = "31415";
    qDebug()<<"old String is =" <<myStr;
    int myStr_int = myStr.toInt();
    myStr_int +=1;
    qDebug()<<"New int value is =" <<myStr_int;

Trying with real vlaues

    QString myStr = "99.99";
    qDebug()<<"old String is =" <<myStr;
    int myStr_int = myStr.toDouble();   //  And:100  [.toFloat() ]
    myStr_int +=1;
    qDebug()<<"New int value is =" <<myStr_int;

My current project requirement expects me to code in Qt C++ [ As I've mentioned earlier that my mind always approaches the solution of a program in Python first because of spending more time in coding in Python than C++]

So we are totally in opposite about the way to do: programming C++ but thinking the program with Python in mind is, for me, the worst way to do.

C++ and python are so far apart in almost every aspect of programming, I can't see how this can work.
If we are only talking about validating an algorithm, why not. But transposing from Python to C++ is not a simple matter. That alone amounts to a new development.

You are assigning ASCII value of 6 to the last character of string. Please refer to ASCII chart online. To simply answer your question, you can add '0' to ur last_dig. That should work.

 myStr[myStr_sz-1] = last_dig + '0'; 

But why are u doing like this? What if the last digit is 9? When u add 1, you will need to add the second last digit as well. A better solution would be to completely convert the string to digit, do the arithmetric operation, and then convert it back to QString

@Swati777999 said in Operations with QString and int:

With this modified code , I got the following result-

It is doing what you have coded.

QString myStr = "31415";
 int myStr_sz = myStr.size(); // => myStr = 5
 int last_dig=myStr[myStr_sz-1].digitValue(); // => last_dig = 5
 last_dig+=1; /// => last_dig = 6
 myStr[myStr_sz-1] = last_dig;  // change  myStr[myStr_sz-1] from '5' to '\x06'
 qDebug()<<"New String is =" <<myStr;

EDIT: you have to understand that 5 != '5', the ASCII code for 5 is 57 or '\x35'

EXAMPLE-1

int x = 56;
  QString str = QString::number(x);
  qDebug()<<"x = " <<str; // x ="56"

Using Example 1 -
I modified the code

 ```
 QString myStr = "31415";
 qDebug()<<"old String is =" <<myStr;  //31415
 int myStr_sz = myStr.size(); // => myStr = 5
 int last_dig=myStr[myStr_sz-1].digitValue(); // => last_dig = 5
 last_dig+=1; // => last_dig = 6
 qDebug()<<"incremented last dig is="<<last_dig;  // 6
 QString str_last =QString::number(last_dig);  
 qDebug()<<"incremented last dig after converting to string is="<<last_dig; // ==> 6
 myStr[myStr_sz-1] = last_dig; 
 qDebug()<<"New String is =" <<myStr;

I am getting the same old result.

Another way I'm thinking is that, popping out the last digit from the string and appending the incremented last digit . I tried it but didn't work. Please give suggestion .

It's not entirely clear, but from the wording of the original post (increase the last digit by one) and then in a subsequent message saying it should work with strings that contain floating-point numbers too, I think @Swati777999 wants '35.456' to become '35.457', for example.

Yes, actually my true intention for putting this Question was about dealing with rounding of real values but I also wanted to be clear about the string and int conversion.

template<typename T>
QString addOne(const QString &string)
{
    auto value = std::is_floating_point<T>::value ? string.toDouble() : string.toInt();
    return QString::number(++value);
}

int main(int argc, char *argv[])
{
    qDebug() << addOne<int>("12345") << addOne<float>("1234.56");
}

Yes, it works absolutely fine. I was trying this with real values say - myStr = " 314.19"

Please again, don't program in C++ as you would do it in python, this will not work!
There is no implicit convertion from string <=> real or string <=> integer in C++.
I you want to program in python style, use python not C++ or you will only go frustrated.

With this modified code , I got the following result-

It is doing what you have coded.

QString myStr = "31415";
 int myStr_sz = myStr.size(); // => myStr = 5
 int last_dig=myStr[myStr_sz-1].digitValue(); // => last_dig = 5
 last_dig+=1; /// => last_dig = 6
 myStr[myStr_sz-1] = last_dig;  // change  myStr[myStr_sz-1] from '5' to '\x06'
 qDebug()<<"New String is =" <<myStr;

EDIT: you have to understand that 5 != '5', the ASCII code for 5 is 57 or '\x35'

@Swati777999 said in Operations with QString and int:

Also, think about what should happen if last number is 9?

Yes, this is in my mind, it's the next stage of this trial but before that, I need to be sure about the working of incrementation.

what's wrong with

QString myStr = "31415";
int myInt = myStr.toInt();
myStr = QString::number(++myInt);

?

QString myStr = "31415";
 int myStr_sz = myStr.size();
 int last_dig=myStr[myStr_sz-1].digitValue();
 last_dig+=1;
 myStr[myStr_sz-1] = last_dig;
 qDebug()<<"New String is =" <<myStr;

With this modified code , I got the following result-

Though it's not the desired output , yet I loved the appearance of Spade from nowhere!

I was working in Python before starting to work in Qt, even though I have studied c++ before

Again Qt is not a programming language, Qt is a framework developped in C++.
Like django is a web framework developped in Python.

This has not modifed myStr . Can someone tell me where I am going wrong?

Qt is a C++ framework, so please take time to learn some C++ basics.
It looks to me as you are expected Qt/C++ working as another language like Python or JavaScript.
But that's not the case, and will never be!

Each programming language has his own way to work, so please learn C++ if you want to use Qt or maybe PySide (Qt binding for Python) is a better alternative for you.

This has not modifed myStr

Why should it? You do not modify it.
You also need to replace the last character in myStr with the new number.
Use https://doc.qt.io/qt-5/qstring.html#operator-5b-5d

Also, think about what should happen if last number is 9?