For this question, how can I sum the last four? Cause I always get segmentation fault. Can someone teach me about memory? Thanks a lot.

you will implement the following two functions in assembly language:

void value(int v) int sum(); 

A call to the function sum returns the sum of the last four values passed to the function value. For example, the following sequence of function calls will output The sum of the last four is 47:

 value(7); value(3); value(-8); value(19); value(22); value(14); int s = sum(); printf("The sum of the last four is %d ", s); 

The last four calls to value were passed values of -8,19,22,14. The sum of those four values is 47. Values prior to the last four are ignored.

If fewer than four calls have been made to value, return the sum of the numbers that have been passed to value, however many calls have occurred. For example this code will output The sum of the last four is 10:

 value(7); value(3); int s = sum(); printf("The sum of the last four is %d ", s); 

If value has not been called, yet, sum should return a value of zero.

Use only registers r0-r3. Do not use any other registers.