Function is much important when we have to do a long project. Let we have a math function (sum, sub,mul etc.) in our project we need the same calculation several times. if we have a function. We can do it by a single line (by calling the function). Otherwise we will have to rewrite the same code of calculation again. And function got arbitrarily long. Above this reason we use function in C program and we don’t write all codes in main () function.
There's more than one Algorithms to solve any Problem.