The most common value to add or subtract from a variable is 1.
Increasing a variable by 1 is called incrementing, and decreasing it by 1 is called decrementing.
C++ includes a ++ increment operator and -- decrement operator to accomplish these tasks:
score++;
my_int--;
These statements increase score by 1 and decrease my_int by 1, respectively. They are equivalent to these more verbose statements:
score = score + 1; my_int = my_int - 1;
The increment operator ++ and decrement operator -- can be used either before or after a variable's name to achieve different results.
An operator placed before a variable's name is called a prefix operator, as in this statement:
++count;
An operator placed after the variable name is called the postfix operator: count++;
The prefix operator occurs before the variable's value is used in the expression. The postfix is evaluated after.
int x = 5; int sum = ++x;
After these statements are executed, the x variable and sum variable both equal 6.
The prefix operator in ++x causes x to be incremented from 5 to 6 before it is assigned to sum.
Compare it to this example:
int x = 5; int sum = x++;
This causes sum to equal 5 and x to equal 6. The postfix operator causes x to be assigned to sum before it is incremented from 5 to 6.
#include <iostream> int main() /*from www. j a v a 2 s . c om*/ { int year = 2018; std::cout << "The year " << ++year << " passes.\n"; std::cout << "The year " << ++year << " passes.\n"; std::cout << "The year " << ++year << " passes.\n"; std::cout << "\nIt is now " << year << "."; std::cout << " Have the Chicago Cubs won the World Series yet?\n"; std::cout << "\nThe year " << year++ << " passes.\n"; std::cout << "The year " << year++ << " passes.\n"; std::cout << "The year " << year++ << " passes.\n"; std::cout << "\nSurely the Cubs have won the Series by now.\n"; return 0; }