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What code have you written to solve your homework? What problems are you having?
Break the problem up into smaller pieces.
How would you take input for 2 integers?
How would you determine whether the 2nd integer is a multiple of the 1st?

nullptr 167

Do you get any error code when searching for updates?
Try temporarily suspending Avast's Shields and see if you get any further with windows update.

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What operating system are you running and what make/model of laptop?
Does windows update get as far as showing how many updates are available?
If so, does it start downloading or installing any updates?

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Try scanning your PC with ESET Online Scanner

then

Download Tweaking.Com - Windows Repair Portable to your Desktop and extract the folder from the zip archive.
Open the folder and run Repair_Windows.exe. Select the Repairs tab and then click on the 'Open Repairs' button.
Select the following Repairs:

  • 03 - Reset Service Permissions
  • 04 - Register System Files
  • 05 - Repair WMI
  • 10 - Remove Policies Set by Infections
  • 17 - Repair Windows Update
  • 26 - Restore Important Windows Services
  • 27 - Set Windows Services to Default Startup

Press the 'Start Repairs' button. When all repairs have completed, you'll receive a prompt to reboot.
Reboot the PC and see if Windows Update will work.

nullptr 167

Seeing as start and last are both int, you just need to cast &a[1].num1 and &a[0].num1 as type int.
start = (int) &a[1].num1;
Or quite simply you could use:
printf("\nsize of structure :%d bytes", sizeof(a[0]) );