I am new to QT, learning through some small programs. I am trying to do arithmetic operations, it is not happening. I am having multiple files. All variables are declared and defined in main.cpp file. In other files I using it with the keyword extern. Even simple arithmetic operations like a = a+1 or a++ is not working. I noticed this issue with a floating point variable first. Now no arithmetic operations are working. I tried by declaring these variables as local to the function and global to the file. still no change. How to tackle this issue? what is the reason for this?