Using C programming and UNIX/Linux terminal. PLEASE DON\'T FORGET TO EXPLAIN THE

Question

Using C programming and UNIX/Linux terminal.

PLEASE DON'T FORGET TO EXPLAIN THE LAST PART!

/*
String constants
Illustrates: string constants, pointers to strings, and array of chars
*/

#include <stdio.h>

int main()
{
char *a = "I am a constant"; // a pointer initialized to point to
// a string constant; value of a can
// be changed; content of string cannot
// be changed
char b[] = "Hello"; // an array of characters (i.e. a string)
// initialized to "Hello"; value of
// b cannot be changed; content of
// string can be changed
// since dimension is not given, string
// is made just big enough to contain
// all the specified characters
char c[] = {'H', 'e', 'l', 'l', 'o', ''};
// equivalent to definition of b
printf("%s %s %s ",a, b, c);
return 0;
}

5. Download the file lab7q5.c from Moodle containing source code which comes from the in-class ex- amples for topic 11 (C Programming - Memory II). Copy lab7q5.c to lab7q5 modified.c. In lab7q5_modified.c, add a statement after the call to printf) that will assign to a[0] and b[O] the character 'X'. (You do not have to show a log of your editing in lab7.txt.) Once your editing is completed, run a diff (1) on the two files (lab7q5.c and lab7q5_modified.c) to show your modifi- cation. Compile and run lab7q5.c. Make sure to use -Wall and -Wextra when you compile, and that there are no warnings or errors generated. Finally, run the resultant executable binary file. Cut and paste into lab7.txt what is produced as a result. In lab7.txt, explain why the modified program produces the output it does. If you do not understand, please ask for assistance from the lab instructor.

Explanation / Answer

#include <stdio.h>

int main()
{
char *a = "I am a constant"; // a pointer initialized to point to
// a string constant; value of a can
// be changed; content of string cannot
// be changed
char b[] = "Hello"; // an array of characters (i.e. a string)
// initialized to "Hello"; value of
// b cannot be changed; content of
// string can be changed
// since dimension is not given, string
// is made just big enough to contain
// all the specified characters
char c[] = {'H', 'e', 'l', 'l', 'o', ''};
// equivalent to definition of b
printf("%s %s %s ",a, b, c);
a[0]='X';
b[0]='X';
return 0;
}

This results in a Segmentation fault and that is because a can't be modified as it is not allocated any memory and you can't access it like this.

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