C中的返回值函数

Question

Hello I'm working on a quick program that generates a master code and the user has to guess the code. When checking the user's guess I use 2 functions one for Exact Matches and the other for close matches (where they got a number that's in the mastercode but not in the right location)

Ex. master code 1 2 3 4

user 2 3 2 4 the output the should show the user has 2 close matches and one exact match. I'm having trouble understanding how to properly return an int.

My ouput just shows the default value of exactMatch and closeMatch when I try to print them in Main. any insight will be greatly appreciated. Thank you.

 #include<stdio.h>
 #include<math.h>
 #include<stdlib.h>
 #include<time.h>
 #define CODELENGTH 4
 #define NUMSYMBOLS 6


 int MasterCode[4];
 int guess[ 4 ];
 int exactMatch;
 int closeMatch=0;

 void genCode (int MasterCode[])
{
int i=0;
int k;
while (i < CODELENGTH){

MasterCode[i] =rand() %NUMSYMBOLS +1;
    i++;

}//end while loop.
for ( k = 0 ; k < 4; k++ ) {
    printf( "%d ", MasterCode[ k ] );
}

printf( "\n" );
}





 void getGuess (int guess[])
{

int number = 0;

printf( "Please enter your list of 4 numbers between 1 and 6: " );
int j;
int k;
for ( j = 0 ; j < 4; j++ ) {
    scanf( "%d", &number );
    guess[ j ] = number;
}

printf( "Your array has these values: " );

for ( k = 0 ; k < 4; k++ ) {
    printf( "%d ", guess[ k ] );
}

printf( "\n" );
 }




 int main (int argc, char **argv)
 {
srand ( time(NULL) );

genCode(MasterCode);
getGuess(guess);
checkExactMatches(MasterCode, guess, exactMatch);
checkCloseMatches(MasterCode, guess, closeMatch);
printf("%d = Ending exactMatches \n", exactMatch);
printf("%d  = Ending closeMatches \n", closeMatch);





 }
 int checkExactMatches (int MasterCode[], int guess[], int exactMatch )
  {
int woot;
for(woot=0; woot<4; woot++){


        if (MasterCode[woot] == guess[woot]){
            printf("Exact Match found \n");
            exactMatch ++;
            printf( "%d = Guess \n" , guess[ woot ]);
            printf( "%d = MasterCode \n", MasterCode[ woot ]);
            printf("%d = exactMatch \n", exactMatch);

        }// end if

        if (MasterCode[woot] != guess[woot])
            printf("No EXACT match \n");


}//end for loop

return exactMatch;
 } // end checkExactMatches



 int checkCloseMatches (int MasterCode[], int guess[], int closeMatch )
  {
int k;
int j;
for(k=0; k<4; k++){

    for (j=0; j<4; j++) {


        if (MasterCode[k] == guess[j]){
    printf("CLOSE Match found \n");
    closeMatch ++;
    printf( "%d = Guess \n" , guess[ j ]);
    printf( "%d = MasterCode \n \n", MasterCode[ k ]);
    printf("%d = closeMatch \n \n", closeMatch);

}// end if

if (MasterCode[k] != guess[j])
    printf("No CLOSE match \n");


    }//end nested for loop
}//end for loop

return closeMatch;
 } // end checkCloseMatches

Answer 1

Getting the value returned from a function is actually really easy, it's basically the same as assigning a value to a variable. In your case, the syntax would be something like this:

int result = checkExactMatches(MasterCode, guess, exactMatch);

result will now hold the value returned by the function.

Answer 2

What you need to do is

• Not pass the count arguments to the function and
• Instead collect the return value of the function in the count

So

checkExactMatches(MasterCode, guess, exactMatch);

becomes

exactMatch = checkExactMatches(MasterCode, guess);

You need to make appropriate changes to the function header and also avoid using global variables.

Answer 3

Note that while arrays are passed by pointer (meaning that the function can modify the pointed-to pointer), ints are passed by value. Therefore, changes to the int within a function only persist for the duration of the function.

You want to use

exactMatch = checkExactMatches(MasterCode, guess);

and in that case you won't have to pass in exactMatch any more.

Answer 4

C passes arguments by value, rather than by reference, so passing int exactmatch into the function creates a duplicate of the data inside exactmatch , so operations done inside the method don't do anything.

What you want to do is remove exactmatch from the argument list, and instead assign it as zero ( int exactmatch=0; at the beginning of the method, remove exactmatch from the global variables, and use something like int resultExact = checkExactMatches(MasterCode, guess); as your function call. You're already returning the answer correctly, you just don't pick up that answer anywhere.