On 11/27/17 7:54 AM, Cai Gengyang wrote:
Input :
count = 0
if count < 5:
print "Hello, I am an if statement and count is", count
while count < 10:
print "Hello, I am a while and count is", count
count += 1
Output :
Hello, I am an if statement and count is 0
Hello, I am a while and count is 0
Hello, I am a while and count is 1
Hello, I am a while and count is 2
Hello, I am a while and count is 3
Hello, I am a while and count is 4
Hello, I am a while and count is 5
Hello, I am a while and count is 6
Hello, I am a while and count is 7
Hello, I am a while and count is 8
Hello, I am a while and count is 9
The above input gives the output below. Why isn't the output instead :
Hello, I am an if statement and count is 0
Hello, I am a while and count is 0
Hello, I am an if statement and count is 1
Hello, I am a while and count is 1
Hello, I am an if statement and count is 2
Hello, I am a while and count is 2
Hello, I am an if statement and count is 3
Hello, I am a while and count is 3
Hello, I am an if statement and count is 4
Hello, I am a while and count is 4
Hello, I am a while and count is 5
Hello, I am a while and count is 6
Hello, I am a while and count is 7
Hello, I am a while and count is 8
Hello, I am a while and count is 9
It's easy to imagine that this sets up a rule that remains in effect for
the rest of the program:
if count < 5:
print "Hello, I am an if statement and count is", count
But that's not how Python (and most other programming languages) works.
Python reads statements one after another, and executes them as it
encounters them. When it finds the if-statement, it evaluates the
condition, and if it is true *at that moment*, it executes the contained
statements. Then it forgets all about that if-statement, and moves on
to the next statement.
--Ned.
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