Program 4

String Manipulation

Due: Monday, March 30

We will be using pointers in assembly language to manage dynamic structures.  We will use syscall 9 to acquire memory space from the heap at run time.  A dynamic string is dynamically allocated to be the proper size and ends in the null character (0)

Write an assembler language program with the following 4 functions:

• Length ($v0, $a0) - returns the length of the referenced string pointed to by $a0 in register $v0.
• Create ($v0, $a0) - returns a pointer in $v0 to the ASCII string that it dynamically allocates and loads with the string pointed to by the pointer in $a0.
• Append ($v0, $a0, $a1) - returns a pointer in $v0 to the dynamic string that results from concatenating the two ASCII strings pointed to by $a0 and $a1.
• Print ($a0) - prints the string pointed to by the pointer in $a0.

The main will perform the following actions

1. Create a string (str1) containing "This is a test".
2. Create a string (str2) containing "of our string routines".
3. Create a string (str3) by appending str1 to str2.
4. Print a title, followed by str1, str2 and str3; all properly labeled.

Write a second program that:

1. Create an empty string (str4).
2. Performs a loop 5 times that:
   a.    Inputs a string from the keyboard (str5) - using memory mapped I/O functions
   b.    Appends str5 to str4
   c.    Prints str4

Write a third program that:

1. Reads a string from a file on one line, reads a string from the next line, concatenates them (without new lines) and print out the new string.