Clicker Questions - 05-More-Strings
Behold the following program in C:
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#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main() {
char s[20];
int i;
for (i = 0; i < 15; i++) s[i] = '0' + i % 10;
s[i] = '\0';
printf("%s\n", s); /* First line*/
for (i = 0; i < 15; i += 4) s[i] = '\0';
for (i = 0; i < 15; i += 3) {
printf("%d-%s\n", i, s+i); /* Lines two through six */
}
strcat(s+7, s+13);
printf("%s\n", s+7); /* Last line */
return 0;
}
This program has seven lines of output. Each clicker question asks for a line of output.
Remember, it’s strcat(destination, source).
Question 1: What is line 1?
Answer
You should write down your work to answer this question. It's easiest to do in a text editior, but if you don't have access to a text editor while doing this, then use a piece of paper. Trying to do this in your head will be confusing.Start with writing down the characters in s, using an asterisk for the null character:
s: 01234567891234*Let's label where s+11 is:
s: 01234567891234*
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s
That lets us answer the first question: "1234".
Question 2: What is line 2?
Answer
Now, let's set every fourth character to the null character, starting with character zero:s: *123*567*901*34*And let's label the pointers at s is:
s: *123*567*901*34* | 0That lets us answer the second question: 0-
Question 3: What is line 3?
Answer
Now, let's set every fourth character to the null character, starting with character zero:s: *123*567*901*34*And let's label the pointers at s+3 is:
s: *123*567*901*34* | | 0 3That lets us answer the third question: 3-3
Question 4: What is line 4?
Answer
Now, let's set every fourth character to the null character, starting with character zero:s: *123*567*901*34*And let's label the pointers at s+6 is:
s: *123*567*901*34* | | | 0 3 6That lets us answer the fourth question: 6-67
Question 5: What is line 5?
Answer
Now, let's set every fourth character to the null character, starting with character zero:s: *123*567*901*34*And let's label the pointers at s+9 is:
s: *123*567*901*34* | | | | 0 3 6 9That lets us answer the fifth question: 9-901
Question 6: What is line 6?
Answer
Now, let's set every fourth character to the null character, starting with character zero:s: *123*567*901*34*And let's label the pointers at s+12 is:
s: *123*567*901*34* | | | | | 0 3 6 9 12That lets us answer the sixth question: 12-
Question 7: What is line 7?
Answer
Now, let's label s+7 and s+13:
s: *123*567*901*34*
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s+7 s+13
The strcat() will find the first null character after (s+7). That's at s+8. It then copies the characters from s+13 to the null character, and null terminates. The string now looks like:
s: *123*56734*1*34*
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s+7 s+13
When we print starting at s+6, we get the characters "6734".