Practice Questions

Question 1

The following C code is supposed to calculate the sum of the first n integers. However, there are bugs in this code. Using the pencil-and-paper method, find the bugs on this code. For example, when n = 5 the correct result should be 15. Then, start with n=5 and keep track of each variable in the code.

int sum_first_n_integers(int n)
{
    int i = 1;
    int sum = i;
    
    while(i <= n){
        sum = sum + i;
        i = i + 1;
    }

    return sum;
}

Question 2

Another method to debug the code in the previous question would be to use a log-based method. Recall that the C command to print to standard output (spoiler of one of the next topics: Standard Streams) is:

printf("The variable result is %d\n", var);

This will replace the %d by the current value of var when the this line is reached. Rewrite the previous code including a log-based debugging and find the bugs in the code. You can edit, compile and run the following code snippet for this purpose. In case you do not recall how to compile C code, revisit the section on compiling and running code.

#include <stdio.h>
#include <stdlib.h>

int sum_first_n_integers(int n)
{
    int i = 1;
    int sum = i;
    
    while(i <= n){
        sum = sum + i;
        i = i + 1;
    }

    return sum;
}

int main(int argc, char* argv[])
{
    int n = 5;
    
    int result = sum_first_n_integers(n);
    printf("Sum result is: %d\n", result);

    return EXIT_SUCCESS;
}

clang -Wall int_sum.c -o int_sum

./int_sum

Question 3

Regarding debuggers, define in your own words the meaning of the following key terms:

1. Breakpoints;
2. Step in;
3. Step over;
4. Step out.