An electric device delivers a current of [tex]$15.0 A$[/tex] for 30 seconds. How many electrons flow through it?
Answer (2)
Evaluate the expression step by step, tracking changes in a, b, and c.
a++++b: a is used as 4, then incremented twice. b is used as 5. So, 4 + 5 = 9. a becomes 6.
c++: c is used as 7, then incremented. So, c becomes 8.
--a: a is decremented twice, so a becomes 4.
++b: b is incremented twice, so b becomes 7.
b--: b is used as 7, then decremented. So b becomes 6.
The expression becomes c = 9 - 8 - 4 + 7 - 6 + c.
The current value of c is 8, so c = 9 - 8 - 4 + 7 - 6 + 8.
Calculate the final value of c: c = 9 - 8 - 4 + 7 - 6 + 8 = 6.
The final answer is 6 .
Explanation
Understanding the Problem We are given a code snippet with pre-increment and post-increment operators. We need to determine the final value of the variable 'c' after the execution of the given line of code. The initial values are a = 4, b = 5, and c = 7.
Breaking Down the Expression The expression to evaluate is: c = a + + + + b − c + + − − a + + + b − b − − + c Let's break it down step by step, keeping track of the changes in a, b, and c.
Step-by-step Evaluation
a++++b : 'a' is used as 4, then incremented by 2. 'b' is used as 5. So, 4 + 5 = 9. 'a' becomes 6.
c++ : 'c' is used as 7, then incremented. So, 'c' becomes 8.
--a : 'a' is decremented by 2, so 'a' becomes 4.
++b : 'b' is incremented by 2, so 'b' becomes 7.
b-- : 'b' is used as 7, then decremented. So 'b' becomes 6.
The expression becomes c = 9 − 8 − 4 + 7 − 6 + c .
The current value of 'c' is 8, so c = 9 − 8 − 4 + 7 − 6 + 8 .
Calculate the final value of 'c': c = 9 − 8 − 4 + 7 − 6 + 8 = 6 .
Final Result Therefore, the final value of c is 6. The values of a and b are 4 and 6 respectively.
Examples
Understanding increment and decrement operators is crucial in programming for tasks such as loop counters, memory management, and updating variable states efficiently. For example, in game development, these operators can be used to update player scores, track lives, or manage resources dynamically. Similarly, in data processing, they can be used to iterate through data structures or update counters during analysis, ensuring efficient and concise code execution.
To find the number of electrons flowing through a device with a current of 15.0 A over 30 seconds, we first calculate the total charge using Q = I × t , which gives 450.0 C . Then, dividing by the charge of a single electron (approximately 1.6 × 1 0 − 19 C ), we find that approximately 2.81 trillion electrons flow through the device. This illustrates the vast number of electrons involved in even a simple electric current.
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