Boolean Type and Expressions in Python
Clarifications on Strings
•
I received a number of queries
•
Here are some explanations. For more details,
please surf the Internet.
1
What’s the difference?
char string1[6] = "apple";
char *string2 = "apple";
2
Example #1
3
char word1[5] = "good";
char word2[4] = "bye";
word1 = word2;
Attempt to change the value of constant
pointer word1!
Not allowed!
strcpy(word1, word2);
×
word1 is not changed.
Characters in array word1 are
changed.
Allowed!
Example #2 (Week 10 Discussion Q5)
4
char *fruit1 = "apple";
char *str1 = "yes";
fruit1 = str1;
fruit1 now points to “bye”.
Allowed!
strcpy(fruit2, str2);
Pink boxes “apple” are in read-
only memory; cannot
overwrite them with “bye”.
Not allowed!
char *fruit2 = "apple";
char *str2 = "yes";
Concept of Boolean type expressions in Python, understanding how they can only have True or False values. Learn about generating boolean results through comparisons of numerical values or strings, and see examples of doing numerical and string comparisons in Python.
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Presentation Transcript
Clarifications on Strings I received a number of queries Here are some explanations. For more details, please surf the Internet. 1
Whats the difference? char string1[6] = "apple"; char *string2 = "apple"; The characters inside the array can be changed. string1 a p p l e \0 The value inside this box, which is the address of the location that contains a , cannot be changed. For ease of reference, we shall call string1 a constant pointer/address. string2 a p p l e \0 string2 is a pointer whose value can be changed. That is, it can point to a different location. However, this string literal is residing in read-only memory, so its contents cannot be changed. 2
Example #1 char word1[5] = "good"; char word2[4] = "bye"; word1 \0 g o o d word1 = word2; word2 \0 b y e Attempt to change the value of constant pointer word1! Not allowed! strcpy(word1, word2); word1 o y e \0 \0 d \0 g b o word1 is not changed. Characters in array word1 are changed. Allowed! word2 \0 b y e 3
Example #2 (Week 10 Discussion Q5) char *fruit1 = "apple"; char *str1 = "yes"; fruit1 \0 a p p l e fruit1 = str1; str1 \0 b y e fruit1 now points to bye . Allowed! char *fruit2 = "apple"; char *str2 = "yes"; strcpy(fruit2, str2); fruit2 \0 a p p l e Pink boxes apple are in read- only memory; cannot overwrite them with bye . Not allowed! str2 \0 b y e 4
