## Parenthesis matching algorithm

**PARENTHESIS_MATCHING (EQ, VALID)**

This algorithm checks whether the expression EQ written in infix notation is valid or not and assigns TRUE or FALSE to VALID.

**1. Scan EQ from left to right until the end of the equation is encountered:**

**2. If”(“is encountered then: put it in the STACK.**

**3. If the closing bracket is encountered then:**

** (a) If STACK is empty, then Set VALID: = FALSE and return.**

** (b) Pop the “(” from the STACK.**

** [End of If structure.]**

** [End of Step 2 loop.]**

**4. If STACK is empty, then:**

** Set VALID := TRUE**

**7. Else:**

** Set VALID := FALSE**

** [End of If structure.]**

**8. Return**

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