Answer
Assuming that variables $a, b, c,$ and $d$ are stored in memory locations $100,$
$101,102,$ and $103,$ respectively:
$\begin{array}{llll}
{\text {Memory}} & {\text {} } & {\text {Address} } & {\text {} }\\
{\text {Location }} & {\text {Op Code} } & {\text {Field} } & {\text {Comment} }\\
{50} & {\text { LOAD }} & {101} & {\text { Register } R \text { now contains the value of } b} \\
{51} & {\text { ADD }} & {102} & {R \text { now contains the sum } b+c} \\
{52} & {\text { ADD }} & {103} & {R \text { now contains the sum } b+c+d} \\ {53} & {\text { STORE }} & {100} & {\text { And we store that sum into } a}\end{array}$
There are many other possible solutions to the previous and the following
problems, depending on which instructions you choose to use. The previous
solution uses the one-address format. The two- and three-address formats
would lead to different sequences.
Work Step by Step
Assuming that variables $a, b, c,$ and $d$ are stored in memory locations $100,$
$101,102,$ and $103,$ respectively:
$\begin{array}{llll}
{\text {Memory}} & {\text {} } & {\text {Address} } & {\text {} }\\
{\text {Location }} & {\text {Op Code} } & {\text {Field} } & {\text {Comment} }\\
{50} & {\text { LOAD }} & {101} & {\text { Register } R \text { now contains the value of } b} \\
{51} & {\text { ADD }} & {102} & {R \text { now contains the sum } b+c} \\
{52} & {\text { ADD }} & {103} & {R \text { now contains the sum } b+c+d} \\ {53} & {\text { STORE }} & {100} & {\text { And we store that sum into } a}\end{array}$
There are many other possible solutions to the previous and the following
problems, depending on which instructions you choose to use. The previous
solution uses the one-address format. The two- and three-address formats
would lead to different sequences.