Sample output $1$

Enter the gallons used $(-1\mathrm{.}0$ to end$)$: $12\mathrm{.}8$

Enter the miles driven: $287$

The miles $/$ gallon for this tank was $22\mathrm{.}421875$

Enter the gallons used $(-1\mathrm{.}0$ to end$)$: $10\mathrm{.}3$

Enter the miles driven: $200$

The miles $/$ gallon for this tank was $19\mathrm{.}417475$

Enter the gallons used $(-1\mathrm{.}0$ to end$)$: $5$

Enter the miles driven: $120$

The miles $/$ gallon for this tank was $24\mathrm{.}000000$

Enter the gallons used $(-1\mathrm{.}0$ to end$)$: $-1$

The overall average miles $/$ gallon was $21\mathrm{.}601423$

That's all folks $-$ press any key to exit

Sample output $2$

$===========$

Enter the gallons used $(-1\mathrm{.}0$ to end$)$: $-\mathrm{.}5$

You have entered an invalid value for gallons, try again: $-1$

The overall average miles could not be computed $$

That's all folks $-$ press any key to exit

Sample output $3$

$=============$

Enter the gallons used $(-1\mathrm{.}0$ to end$)$: $-\mathrm{.}5$

You have entered an invalid value for gallons, try again: $-1\mathrm{.}5$

You have entered an invalid value for gallons, try again: $0$

You have entered an invalid value for gallons, try again: $10$

Enter the miles driven: $-\mathrm{.}5$

You have entered an invalid value for miles, try again: $0$

You have entered an invalid value for miles, try again: $100$

The miles $/$ gallon for this tank was $10\mathrm{.}000000$

Enter the gallons used $(-1\mathrm{.}0$ to end$)$: $-\mathrm{.}5$

You have entered an invalid value for gallons, try again: $-1\mathrm{.}5$

You have entered an invalid value for gallons, try again: $0$

You have entered an invalid value for gallons, try again: $20$

Enter the miles driven: $250$