Three programming languages whose name is a single letter can cause confusion. You have C, C++, and C#. They seem similar but basically are incompatible with each other. You can write just about anything in C and it was the first language of the 3 to exist. C++ allows you to do many things you can do with C but has additional definitions that C will not recognize. Most C code can be applied to C++ but the reverse is not true. C# is in a similar shape. There is much more to C# that neither C or C++ would recognize. C# can do C-style pointers in a special mode of the language that is never used in practice. About 90% of C++ and its standard library is unrecognizable in C#.
A nearly common syntax is to cut down the time to transition from one to the other. Beyond that, the similarities are purely superficial. C programs can be faster and more comprehensive at a systems level than C++ or C# programs. C++ programs can have greater depth of design definition since it is multi-paradigm. You can create a software program in less time with C# with less error than either C or C++ at a occasional cost of speed.