Function that repeats a given string n times and returns the repeated string

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the funtion should work in the following way :

repeat(3, "foo") s

and returns

"foofoofoo"

we have the following code :

char *repeat(size_t n, char *s) {

  char *array = malloc(sizeof(char) * strlen(s) * (1 + n)); //Q1

  for (int i = 0; i < strlen(s) * n; i++) {  //Q2

    array[i] = s[i % strlen(s)];
  }

  array[strlen(s) * n] = 0;  //Q3

  return array;

}

Q1: does someone know why we write (n+1) anstead of (n) ?
Q2: why to write (strlen(s) * n )
Q3: why to write at the end array[strlen(s) * n] = 0;
Q4: why we dont write free after we allocated the array ?

What I have tried:

.....................................................

Posted 29-May-21 3:27am

Ahmad Qassym

Updated 29-May-21 4:25am

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Patrice T 29-May-21 10:22am

What are your answers to the 4 questions.

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k5054 · Answer 1 · 2021-05-29T03:45:00

Most of your questions can be answered here: C - Strings - Tutorialspoint[^]

As for Q4: Assume that free() makes the previously allocated memory block totally inaccessible going forward. Think about what might happen later in your program if you called free before you return from the function. What can the caller do with the returned pointer?

OriginalGriff · Answer 2 · 2021-05-29T04:25:00

Q1: Because whoever wrote that doesn't know what they are doing: you need the (length times n) + 1 characters to allow for the trailing null.

Q2: So you go round the loop the right number of times.

Q3: Similar to Q1: Because whoever write that doesn't know how to write efficient or even easily readable code.

Q4: See K5054's answer.

Would I write the code like that? No. I'd get the string length once, and use two nested loops and a pointer, or a pointer and the standard library strcpy function in a single loop. Probably the latter.

Function that repeats a given string n times and returns the repeated string

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