Every piece of data lives somewhere in memory. A pointer is a piece of data containing the address of another piece of data. int a = 42; // puts the number 42

Every piece of data lives somewhere in memory. A pointer is a piece of data containing the address of another piece of data. int a = 42; // puts the number 42 somewhere in memory int* p = &a; // gives you the address where that 42 is stored A function with a signature like int f(int n); takes an int as an argument. When you pass it the a above, it is copied in the stack before the function is called. If you change n inside the function, that only affects the value of n inside the function. But let's say you wanted to change what was passed in to it. In that case you would change f to int f(int* p); Now when you pass the a declared above (using &a) you actually have a pointer to a in f i.e. the address where a is stored. If you do *p = 51; inside f, you changed the value of a and that change is visible even after f returns. Hope that helps.