why does it produce error ?

Question

>>>int('3.0')+int('2')

Answer 1

"int" will cast/convert integer looking strings to int type.
"3.0" does NOT look like an int, so will not convert.

You can make it work using float... e.g.

float ('3.0') + float ('2')
float ('3.0') + int ('2')

Answer 2

this is not possible in c due to typecasting