In the printf a number of values may follow the format string. These values are used up by % placeholders in the format string.

The format string is

"Country: %-18s GDP: %,20d\n"

%-18s

the minus in -18 means align left, the 18 means 18 characters are to be used, the s is for string.

%,20d

the comma means include , separator every three digits, the 20 means use 20 characters and align right, d is for decimal.

\n

This starts a new line.

In the Write a number of values may follow the format string. These values are used up by {0}, {1} placeholders in the format string.

The format string is

"Country: {0:-18} GDP: {1,20:n0}\n"

{0:-18}

the minus in -18 means align left, the 18 means 18 characters are to be used.

{1,20:n0}

The 20 means use 20 characters and align right, d is for decimal, the n0 means include , separator every three digits and give zero decimal places.

\n

This starts a new line.