退出函数后，为什么此变量值返回默认值？

Question

I want to move the knight in a chess program. For this reason, I have these two variables( currentRow and currentColumn ) defined on top of all functions including main. (I did this because I wanted these variables as global variables to all functions) as below. Because when the knight moves, its position will change. And this will be the input to its next move.

What I don't understand is when I debug, I saw that these variables are changing in the function but as soon as it exits function, they return to their default values (3 and 4).

Can you tell me how to fix this? Thanks in advance...

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

int currentRow=3;
int currentColumn=4;

int main(void){

...
}

int checkIsEmptyandMoveAccordingly(int moveNumber, int currentRow, int currentColumn){

   if (chessBoard[currentRow+vertical[moveNumber]][currentColumn+horizontal[moveNumber]]==0   && currentRow+vertical[moveNumber]>=0 && currentColumn+horizontal[moveNumber] >=0   ){   //if empty,move to new location

         currentRow+=vertical[moveNumber];
         currentColumn+=horizontal[moveNumber];
         printf("Move randomised to: %d\n", moveNumber);
         printf("Knight has moved to chessBoard[%d][%d].\n",currentRow,currentColumn);
         count++;
         printf("Move count is %d.\n",count);
         chessBoard[currentRow][currentColumn]=1;
         if(!checkIsAroundFUll()){
            moveNumber=randomiseMovement();
            return moveNumber;
         }
         else   { 
              printf("ALL TARGET SPACES ARE VISITED BEFORE. KNIGHT CAN NOT MOVE\n PROGRAM WILL BE TERMINATED!!!\n");
              return -1;
         }
   }

   else if (chessBoard[currentRow+vertical[moveNumber]][currentColumn+horizontal[moveNumber]]==1)  {                                                                                                                                                    //if not empty, randomise again

         printf("Knight CAN NOT MOVE! Target SPACE IS OCCUPIED\n");
         if(!checkIsAroundFUll()){
            moveNumber=randomiseMovement();
            return moveNumber;
        }
         else   { 
              printf("ALL TARGET SPACES ARE VISITED BEFORE. KNIGHT CAN NOT MOVE\n PROGRAM WILL BE TERMINATED!!!");
              return -1;
         }

   }

   else {
         printf("OUT OF BOUNDS!! CAN NOT MOVE. TRYING ANOTHER MOVEMENT");
         if(!checkIsAroundFUll()){
            moveNumber=randomiseMovement();
            return moveNumber;
        }
         else   { 
              printf("ALL TARGET SPACES ARE VISITED BEFORE. KNIGHT CAN NOT MOVE\n PROGRAM WILL BE TERMINATED!!!");

              return -1;
         }
   }
}

Answer 1

int currentRow, int currentColumn are in the function parameter list, so they are local variables. They are hiding the global ones with the same names.

Answer 2

Your function has new variables currentRow and currentColumn declared as parameters to the function. If you want to update the global variables, remove these parameters (and don't pass them when you call the function) and you should see the globals update.

What you're doing is shadowing the global variables. With the right compiler warning enabled (which varies by compiler) you would be told about this error.

Try compiling with -Wall -Werror if you are using gcc.

Answer 3

Your function is changing local copies. When you pass them to the function, they pass by value, the function creates local copies, and the local scope overrides the global scope. If you want to reference global variables, don't pass them into your function, just access them from there.