What is the exact output of the following program segment?

Please enter just the output as it will appear; do not enter any other words in your answer or any spaces before or after your answer. No part marks.

int counter $=10$;

while $($counter $15)$

$\{$

switch $($counter $\%10-1)$

$\{$

case $0$ :

cout $<mtext\; id="EditorElement\_1803496"></mtext><mi\; id="EditorElement\_1803497">\text{'}</mi>$z$\text{'}$;

break;

case $1$:

cout $<mtext\; id="EditorElement\_1803523"></mtext><mi\; id="EditorElement\_1803524">\text{'}</mi>$a$\text{'}$;

break;

case $2$:

case $8$:

cout $\text{'}\text{'}$t$\text{'}$;

break;

case $3$:

cout $<mtext\; id="EditorElement\_1803358"></mtext><mi\; id="EditorElement\_1803359">\text{'}</mi>$b$\text{'}$;

case $4$: case $9$:

cout $<mtext\; id="EditorElement\_1803386"></mtext><mi\; id="EditorElement\_1803387">\text{'}</mi>$x$\text{'}$;

break;

case $5$:

cout $<mtext\; id="EditorElement\_1803413"></mtext><mi\; id="EditorElement\_1803414">\text{'}</mi>$c$\text{'}$;

break;

case $6$:

cout $\text{'}z\text{'}$;

break: