Learn C++

A constant  is a value which can not be modified. As in C, we can have literal constants using #define and we can have enums and we can define a variable to be const .  Let us look at const variables here. By declaring a variable as const , we ensure that it is not modified accidentally. Any modification to a constant will give a compilation error. A const should always be initialized while defining. In the program below,  assignment to pi gives a compiler error because pi is defined as const and code is trying to modify this. int main () { const float pi = 22.0/7 ; int radius = 12 ; radius ++ ; /*ok*/ pi = 3.14 ; /*error*/ }   Constant parameters to functions Even function parameters can be const ant. We have earlier discussed that making a reference parameter as constant will avoid the function from accidentally modifying the argument. void printnum ( int & n) { cout << n ++ ; } void printnum2 ( const int &...

In good old days, C programmers would use preprocessor directive to define constants. e.g. #define s 10 But we know now that, as compiler never gets to see these, preprocessor statements are error prone. Hence we have const s. A constant - defined with keyword const promises that this entity is never going to change. And if we accidentally modify a const, compiler throws an error. Let us look at an example. #include<iostream> using namespace std; int main () { int a = 10 ; const int b = 12 ; a ++ ; b = 18 ; } When we compile this program, compiler tells us that default.cpp: In function ‘int main()’: default.cpp:8:7: error: assignment of read-only variable ‘b’      b = 18; So it is catching the error that we are trying to modify a const. Whenever a local variable or parameter need not be modified, declare it as a const.  Yes, we can make even parameters as constant. We can make objects constant or even me...