Q Why do you need to allocate memory at runtime?
A Very often, you don't know the exact sizes of arrays until your program is being run. You might be able to estimate the sizes for those arrays, but if you make those arrays too big, you waste the memory. On the other hand, if you make those arrays too small, you're going to lose data. The best way is to allocate blocks of memory dynamically and precisely for those arrays when their sizes are determined at runtime. There are four C library functions, malloc(), calloc(), realloc(), and free(), which you can use in memory allocation at runtime.
Q What does it mean if the malloc() function returns a null pointer?
A If the malloc() function returns a null pointer, it means the function fails to allocate a block of memory whose size is specified by the argument passed to the function. Normally, the failure of the malloc() function is caused by the fact that there is not enough memory to allocate. You should always check the value returned by the malloc() function to make sure that the function has been successful before you use the block of memory allocated by the function.
Q What are the differences between the calloc() and malloc() functions?
A Basically, there are two differences between the calloc() and malloc() functions, although both of them can do the same job. The first difference is that the calloc() function takes two arguments, while the malloc() function takes only one. The second one is that the calloc() function initializes the allocated memory space to 0, whereas there is no such guarantee made by the malloc() function.
Q Is the free() function necessary?
A Yes. The free() function is very necessary, and you should use it to free up allocated memory blocks as soon as you don't need them. As you know, memory is a limited resource in a computer. Your program shouldn't take too much memory space when it allocates blocks of memory. One way to reduce the size of memory taken by your program is to use the free() function to release the unused allocated memory in time.
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