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  lt iostream gt  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 lt  lt 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

User · Answer

Here   int y   year-1  100  int c  year-1  100     you declare and initialize the variables y  c  but you don t used them at all before they run out of scope  That s why you get the unused message   Later in the function  y  c are undeclared  because the declarations you made only hold inside the block they were made in  the block between the braces

User · Answer

Here s a simplified example based on of your problem   if  test      begin scope 1     int y   1      end scope 1 else     begin scope 2     int y   2   error  y is not in scope    end scope 2 int x   y   error  y is not in scope   In the above version you have a variable called y that is confined to scope 1  and another different variable called y that is confined to scope 2  You then try to refer to a variable named y after the end of the if  and not such variable y can be seen because no such variable exists in that scope   You solve the problem by placing y in the outermost scope which contains all references to it   int y  if  test         y   1     else        y   2    int x   y    I ve written the example with simplified made up code to make it clearer for you to understand the issue  You should now be able to apply the principle to your code

User · Answer

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  lt  lt  y  lt  lt  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  lt  lt  y  lt  lt  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

User · Answer

include  lt iostream gt  using namespace std  class matrix       int a 10  10  b 10  10  c 10  10  x y i j      public           void degerler            void ters       void matrix  degerler         cout  lt  lt   Satirlari giriniz     cin  gt  gt  x      cout  lt  lt   S  tunlari giriniz     cin  gt  gt  y      cout  lt  lt   Ilk matris elamanlarini giriniz  n n       for  i 1  i lt  x  i                  for  j 1  j lt  y  j                          cin  gt  gt  a i  j                       cout  lt  lt   Ikinci matris elamanlarini giriniz  n n       for  i 1  i lt  x  i                  for  j 1  j lt  y  j                          cin  gt  gt  b i  j                      void matrix  ters         cout  lt  lt   matrisin tersi n       for  i 1  i lt  x  i                  for  j 1  j lt  y  j                  if i  j            b i  j  1            else     b i  j  0          float d k      for  i 1  i lt  x  i              d a i  j           for  j 1  j lt  y  j                  a i  j  a i  j  d              b i  j  b i  j  d                for  int h 0  h lt x  h                          if h  i               k a h  j                  for  j 1  j lt  y  j                                         a h  j  a h  j - a i  j  k                       b h  j  b h  j - b i  j  k                              count  lt  lt  a i  j   lt  lt                count  lt  lt  endl        int main         int secim      char ch          matrix m      m degerler        do            cout  lt  lt   se  iminizi giriniz n       cout  lt  lt    1  matrisin tersi n       cin  gt  gt  secim      switch  secim                case 1              m ters                break            cout  lt  lt    nBaska bir sey yap n        cin  gt  gt  ch            while  ch    n        cout  lt  lt    n       return 0

User · Answer

You need to declare y and c outside the scope of the if else statement  A variable is only valid inside the scope it is declared  and a scope is marked with        include  lt iostream gt   using namespace std     Using the Gaussian algorithm  int dayofweek int date  int month  int year     int d date   int y  c  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       int main     cout lt  lt dayofweek 19 1 2054    return 0

[c++] 'was not declared in this scope' error

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