Question

My question that needs an answer is this:

Can the C++ compilers catch the mistake of using an "=" instead of the comparison operator "==".

Show code how you can test this using an if statement in C++, write a small program to demonstrate it.

If the compiler does not catch the mistake how would one go about ensuring they are using the correct syntax for the comparison operator?

Thank you

Answer 1

• = is an assignment operator which is used to assign a value to a variable
• == is a conditional operator which is used to check if both the variables/ values are equal

  #include <iostream>
  
  using namespace std;
  
  int main()
  {
      int x = 20;
      int y = 18;
      if (x = y) //TYPO
      {
        cout << "x is equal to y";
      }
      else
       cout << "x is not equal to y";
      cout <<x;
      cout << y;
      
  
      return 0;
  }

• Consider the above program, there we have a typo in if condition. I used '=' in place of '=='
• Whenever if-statement gets executed, x is assigned the value of y and until y is not equal to zero we get the statements inside if clause executed. The output of the program will be as follows
• x is equal to y 18 18
• if we make the value of y= 0 then the program will inside if clause x is assigned the value of y(which is 0) and as if(x) is zero we get x is not equal to y as output.

• Running a modern compiler at the highest warning level will cause it to issue a warning when an assignment is used in a conditional statement or a note that the statement does nothing when an equality test is used instead of an assignment outside of a conditional. This is one issue that is essentially fixable -- if you use the higher warning levels.

• So programmers must be careful while using == operator.