Module 11: C Language Strings

Question 1

String

Answer 1

an array of characters terminated by a null character ‘\0’

Question 2

String literal

Answer 2

a string in “double quotes”; a read-only string that cannot be edited once created

Question 3

Standard C library

Answer 3

library of functions that comes with all C compilers (except for LCC) for your use

Question 4

Editing a pointer to a string literal

Answer 4

don’t!
undefined results
on some compilers it works (LCC)
on other compilers, the data in the data in the array is treated as read-only or “constant”

Question 5

character array vs. string vs. pointer to the string

Answer 5

string:
char my_string[] = {‘T’,’o’,’m’,’\0’}

pointer to string:
char* my_string_ptr = “Tom”;
you cannot edit a pointer to a string literal

arrays of strings:
this is an array of strings in C:
char my_2D_array[3][4] = {{‘i’,’\0’}, {‘a’,’m’,’\0’}, {‘t’,’o’,’m’,’\0’}} ;

this is just a 2D array of characters in C (notice no NULLs)
char my_2D_array[3][4] = {{‘i’}, {‘a’,’m’}, {‘t’,’o’,’m’}} ;

Question 6

Passing a 2D array in C

Answer 6

*Note: absence of row number is permissible in 2D array declaration, but absence of column number is not permissible in 2D array declaration

In reality, our function is receiving a memory address. Dereferencing with [] is automated pointer arithmetic. By providing the # of columns in the 2D array, we are telling the compiler how many rows in memory to advance each time the pointer is dereferenced

Question 7

3 possible places to store data in C

Answer 7

stack: local variables, arguments, returns
global region: global vars, static vars
heap: dynamic space

Question 8

strlen()

Answer 8

only counts characters up to but not including the first ‘\0’ although space is allocated as asked for

Question 9

By providing the # of columns in the array…

Answer 9

we are telling the compiler how many rows in memory to advance each time the pointer is dereferenced using the first [] operator

Question 10

array of pointers

Answer 10

integer pointer
int var[] = {10, 100, 200};
int i, *ptr[MAX];
for (i = 0; i < MAX; i++) {
ptr[i]=&var[i]; /*assign the address of integer.*/
}

String pointer:
char *names[] = { “Zara Ali”, “Hina Ali”, “Nuha Ali”, “Sarah Ali”};

Question 11

Pointers to pointers

Answer 11

often used in C to receive addresses of arrays of pointers to strings
int a = 1;
int * a_ptr = &a;
int ** a_ptr_ptr = &a_ptr;
Dereferencing:
char I_array[] = {'I', '\0'};
char Am_array[] = {'a', 'm', '\0'}
char Tom_Array[] = {'T', 'o', 'm', '\0'}
char * array_of_ptrs[3] = {I_array, Am_array, Tom_Array};
char** ptr_to_ptr = array_of_ptrs;
ptr_to_ptr[0] => I_array
ptr_to_ptr => 'I'

Recall the two strings that we can use inside main() via argv[]