'was not declared in this scope' error

Question

So I was writing this simple program to calculate the day of any date using the Gaussian algorithm found here.

#include <iostream> using namespace std;  //Using the Gaussian algorithm int dayofweek(int date, int month, int year ){     int d=date;     if (month==1||month==2)         {int y=((year-1)%100);int c=(year-1)/100;}     else         {int y=year%100;int c=year/100;}     int m=(month+9)%12+1;     int product=(d+(2.6*m-0.2)+y+y/4+c/4-2*c);     return product%7; }  int main(){     cout<<dayofweek(19,1,2054);     return 0; } 

It's a very simple program and what's even more puzzling is the output.

:In function  dayofweek(int, int, int)’: :19: warning:  unused variable ‘y’ :19: warning: unused variable ‘c’ :21: warning: unused variable ‘y’ :21: warning: unused variable ‘c’ :23: error: ‘y’ was not declared in this scope :25: error: ‘c’ was not declared in this scope 

It says that my variable is unused but then says that it isn't declared? Could anyone please tell me whats wrong.

Answer 1

The scope of a variable is always the block it is inside. For example if you do something like

if(...) {      int y = 5; //y is created } //y leaves scope, since the block ends. else {      int y = 8; //y is created } //y leaves scope, since the block ends.  cout << y << endl; //Gives error since y is not defined. 

The solution is to define y outside of the if blocks

int y; //y is created  if(...) {      y = 5; }  else {      y = 8; }   cout << y << endl; //Ok 

In your program you have to move the definition of y and c out of the if blocks into the higher scope. Your Function then would look like this:

//Using the Gaussian algorithm int dayofweek(int date, int month, int year ) {     int y, c;     int d=date;      if (month==1||month==2)     {          y=((year-1)%100);          c=(year-1)/100;     }     else     {          y=year%100;          c=year/100;     } int m=(month+9)%12+1; int product=(d+(2.6*m-0.2)+y+y/4+c/4-2*c); return product%7; }