Variables in Programming and Algebra

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Now that you know what a variable is, we will clarify a common area of confusion between algebra and programming.

In algebra, you can have a statement like this:

x = 2 + 3

This is a "truth-statement" that the variable x is equal to 2+3 or 5.

Similarly, in programming, you can write int x = 2 + 3 and the variable x will end up as the integer 5. However, there's a big difference between the two statements, as will now be seen.

What if you faced the following two statement together?
x = 2 + 3
x = 11

In algebra, you would immediately recognize that this is impossible. x cannot be both 2+3 and 11 since they're not equal. However, in programming, = is not a statement of truth, it's an action that assigns a value to a variable.
So you can assign 2+3 to x and then afterwards assign 11 to x, and x will now be set to 11 instead of 5.

Equality Check
If you wanted to check if something was equal in programming, you use ==. For example:

int x = 2 + 3; //assignment
x == 11; //this would be false

Review this:

  • = assignment
  • == equality check


After the following code runs, what number will sum equal?

int x = 2;
int y = 5;
x = 100;
int sum = x+y;

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  • Enter Integer or Decimal Answer: I expect int sum == answer

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  • You say "In the following code, what number will sum equal?"
    It would be better to say "In the following code, what number will sum become?"
    Also, you should give an extra example of multi-line assignment of variables before testing student understanding

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  • It's easy. Forget the int x = 2 and go to x = 100 and add the y to the x.

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  • In the code why it is written
    int x = 2;
    int y = 5;
    x = 100; .Can anyone tell me why data type int is not written befor x=100;

  • As mentioned on the previous page, you need to declare a variable's type the first time, but afterwards you can use it without re-mentioning what type it is.

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  • When you're ready, check out Algorithms

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  • This was my hardest challenge yet...How does 100 + 5 = 105 if x=2???? Computers are DU|\/|@$$3$ !!!! If X(2)=100 And X(1)=2 and Y(5) then wouldn't x+x+y =107? the only place xxy ever made sense was in Klinefelter syndrome! :p

  • Got confused here since x = 100; wasn't given any data type.

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