what's more convenient in control structure is it if-else or switch ??? or both are convenient ??

Answer 1

both: depends on use cases...

'switch' allows to avoid lot of 'else if', if conditions are just to check a variable against many values ^^

Answer 2

Use `switch` when you validate a value against one or more finite values. C++ does not support chained expressions evaluation or range of values evaluation in `switch` cases (some compiler provides it as extension e.g. gcc - http://gcc.gnu.org/onlinedocs/gcc/Case-Ranges.html)

Use `if..else if..else` when you need to validate against range of values, when there is need to evaluate chained expressions, or when you need to use the benefits of short circuit evaluation - https://softwareengineering.stackexchange.com/questions/325009/short-circuit-evaluation-is-c

I personally think it's not a matter of convenience, it's a matter of choosing one that was meant for the purpose.