C language: Need an explanation for errors in using function

Question

I'm an absolutely newbie to both this site and programming so please be patient with me. I decided to start learning programming by learning C. Now, I still know nothing outside of stdio.h . Anyway, I've now come across a new topic, which is function and I would like to try using it to do something.

However, I've never got the chance to know whether my algorithm is right or not due to the errors while compiling and I really don't understand what the compiler's error message is trying to tell me. I don't know what caused the errors. Therefore, I need someone to have a look at my code and guide/explain/teach me, anything.

I'm trying to print out X and O in chessboard manner by using a function and here's my code.

---

int function_X;                                                         
int function_O;                                                               
int size_controller;                                                          

main()                                                            
{                                                                             
    int i;                                                                     
    int j;                                                                     
    int width;                                                                
    int height;

    clrscr();                                                                  

    printf("Width: \n");                                                       
    scanf("%d", &width);

    printf("Height: \n");                                                      
    scanf("%d", &height);

    for(j=0; j<height; j++)                                                   
    {                                                                          
        for(i=0; i<width; i++)                                                  
        {                                                                      
            if(size_controller(i) )                                              
            {                                                                 
                printf("\n");                                                     
            }                                  

            if(function_X(i, j) )                                              
            {           
                printf("X");                                                    
            } 

            if(function_O(i, j) )                                                      
            {                                                                
                printf("O");                                     
            }                                                                
        }                                                                  
    } 

    return 0;
}


int size_controller(int i)                                                    
{                                                                           
    if(i%width == 0)                                                           
    {                                                                          
        return 1;                                                               
    }                                                                          
    else                                                                       
    {                                                                          
        return 0;                                                              
    }                                                                         
}                                                                             


int function_X(int i, int j)                                                 
{                                                                             
    if((j%2 != 0) && (i%2 != 0) || (j%2 == 0) && (i%2 == 0))                   
    {                                                                          
        return 1;                                                               
    }                                                                          
    else                                                                      
    {                                                                          
        return 0;
    }   
}

int function_O(int i, int j)                                                  
{                                                                             
    if((j%2 != 0) && (i%2 == 0) || (j%2 == 0) && (i%2 != 0))                  
    {                                                                          
        return 1;                                                               
    }                                                                        
    else                                                                     
    {                                                                          
        return 0;                                                             
    }                                                                      
}                                                                          

---

When I tried to run the program, the compiler declared 7 errors and 1 warning:

Error 01.C 27: Call of nonfunction
Error 01.C 32: Call of nonfunction
Error 01.C 37: Call of nonfunction
Error 01.C 48: Type mismatch in redeclaration of 'size_controller' Error 01.C 49: Undefined symbol 'width'
Warning 01.C 57: Parameter 'i' is never used
Error 01.C 60: Type mismatch in redeclaration of 'function_X'
Error 01.C 72: Type mismatch in redeclaration of 'function_O'

Please help me!

Answer 1

Change these (which look like ordinary variables):

int function_X;                                                         
int function_O;                                                               
int size_controller;

To these (which look like function declarations):

int size_controller(int i, int width); /* Needs width parameter. */
int function_X(int i, int j);
int function_O(int i, int j);

But the only truly sensible advice is to get hold of a decent book and study, these really are problems you could have avoided.

Answer 2

The following is declaring a variable:

int function_X;                                                         

You probably want to declare a prototype for the function:

int function_X(int, int);

Alternately, you can place the whole main() function at the bottom of your source file, so that the functions you call are declared above it. Then when the compiler gets to your main() function, it will have already seen the functions declared and knows how to call them. Doing this also avoids having to repeat the function arguments twice, once in the prototype declaration and once in the function definition.

Answer 3

Your forward declarations are wrong.

int function_X;                                                         
int function_O;                                                               
int size_controller;

are actually declarations of functions (with parameters), so they should be

int size_controller(int i);     
int function_X(int i, int j);  
int function_O(int i, int j);

As you declared them, they are variables and the compiler gets confused when you try to call them.

Answer 4

You have to change two things:

1)AS above suggested by,change function Declaration as above

2)Declare the width variable as global means declare it above main().Not in main().

By doing these two changes it will definitely work..