You have to modify the script. For example does the first script set wlan1 into monitor mode. If you only have wlan0, then you have to modify the script.
./1 => Puts wlan0 into monitor mode
./2 => List available wifi networks and enter numer to start capturing handshake and deauthenticating
./3 => Usually you dont use this manually, you just use ./1 once, then ./2 for each network and ./4 to set wifi card out of monitor mode
./4 => Delete the newly created interface, so stop monitor mode
Why in C? Why not just use bash, especially because you use linux binaries instead of native functions from linux api?!
Because i like C and wanted to use C, it's not about efficiency, especially because i call bash, i could have done the same just in bash, but it's not as much fun. I used this project to get used to some basic functions in C.