I have the following questions concerning the differences between the four options: What is the main difference between the four options? Which of the above support int64_t or long long without suffix LL. I want a data type of the range 2^63 - 1 If your answer to my second question is not C(gcc 4.3.2) , whether the code I write in C(gcc 4.3.2) for C language will be valid in rest of the three options or do I have to modify something, then what will be those modifications.