1st year student: Tracing a program by hand

[BrownianMan]

Hey, new to the forum.

I'm currently taking my first programming course, and in one of the assignments, I was asked to trace the following Fortran77 program fragment by hand and determine the final values for n and m:

integer n, m, k, j
n = 0
m = 0
do k = 1, 3
    do j = k, 1, -1
        n = n + j
    end do
    m = m + k
end do
print*, n
print*, m

I was only able to get this far:

n m k j
0 0 1 1
1 1 2 0
3 3 3 2


How should I approach it from here?

 

[rootX]

You are not considering all cases

(
k=1
j=1
)
m=?
n=?

(
k=2
j=2
)
m=?
n=?

(
k=2
j=1
)
m=?
n=?

(
k=3
j=3
)
m=?
n=?

(
k=3
j=2
)
m=?
n=?

(
k=3
j=1
)
m=?
n=?

 

[Mene]

Hello, welcome to the forum! It's great to hear that you are taking your first programming course and are already tackling assignments like this. Tracing a program by hand is a valuable skill that can help you understand the flow of a program and identify any potential errors.

In this case, you have correctly traced the first two iterations of the outer loop (k = 1 and k = 2). To continue, you will need to go back to the beginning of the inner loop (j = k) and trace it for the third iteration of the outer loop (k = 3).

For k = 3, the inner loop will start with j = 3 and count down to 1 (since it is a negative increment). So, for the third iteration, the values of n and j will be 6 and 3 respectively. Then, when the outer loop completes, the final values of n and m will be 9 and 6.

I hope this helps guide you in tracing the program further. Keep practicing and don't hesitate to ask for help if you get stuck. Good luck with your programming journey!