Question

Segmentation Faults Recall what causes segmentation fault and bus errors from lecture. Common cause is an invalid pointer or address that is being dereferenced by the C program. Use the program average.c from the assignment page for this exercise. The program is intended to find the average of all the numbers inputted by the user. Currently, it has a bus error if the input exceeds one number. Load average.c into gdb with all the appropriate information and run it. Gdb will trap on the segmentation fault and give you back the prompt. First find where the program execution ended by using backtrace (bt as shortcut) which will print out a stack trace. Find the exact line that caused the segmentation fault.
Q13. What line caused the segmentation fault?
Q14. How do you fix the line so it works properly?
You can recompile the code and run the program again. The program now reads all the input values but the average calculated is still incorrect. Use gdb to fix the program by looking at the output of read_values. To do this, either set a breakpoint using the line number or set a breakpoint in the read_values function. Then continue executing to the end of the function and view the values being returned. (To run until the end of the current function, use the finish command).
Q15. What is the bug? How do you fix it?
//average.c
#include
/*
Read a set of values from the user.
Store the sum in the sum variable and return the number of values
read.
*/
int read_values(double sum) {
int values=0,input=0;
sum = 0;
printf("Enter input values (enter 0 to finish):\n");
scanf("%d",&input);
while(input != 0) {
values++;
sum += input;
scanf("%d",input);
}
return values;
}
int main() {
double sum=0;
int values;
values = read_values(sum);
printf("Average: %g\n",sum/values);
return 0;
}

Answer 1

Answer:

See Explanation

Explanation:

Q13. Line that caused the segmentation fault?

The segmentation fault was caused by line 15 i.e. scanf("%d",input);

Q14. How the line was fixed?

The reason for the segmentation fault is that the instruction to get input from the user into the integer variable "input" was not done correctly.

The correction to this is to modify scanf("d",input) to scanf("%d",input);

Q15. The bug?

The bug is that the method needs to return two value; the sum of the inputted numbers and the count of the inputted numbers.

However. it only returns the count of the inputted number.

So, the average is calculated as: 0/count, which will always be 0

How it was fixed?

First, change the method definition to: void and also include an array as one of its parameters.

void read_values(double sum, double arr []) {

Next:

assign sum to arr[0] and values to arr[1]

In the main method:

Declare an array variable: double arr [2];

Call the read_values function using: read_values(sum,arr);

Get the sum and values using:

sum = arr[0];

values = arr[1];

Lastly, calculate and print average:

printf("Average: %g\n",sum/values);

See attachment for complete modified program

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