unstable if statement in C

Question

I am trying to write the code of the board game "Mastermind"(homework). I am almost finished writing the main part. Unfortunately, I have an unstable if statement that I can't explain by debugging with Netbeans.

In the following code the if statement of line 58, doesn't always work. The game is like this:

1. The user enters the number of colours that wants to be "randomly" generated
2. The user tries to guess (break the code) the colors.
3. If N=4(for example), then the user enters a sequence of 4 colours trying to guess them. 4.The program checks if he was right or not and gives back feedback.

The 6 colors are: W:White, B:Blue, G:Green, Y:Yellow, P:Purple and R:Red.

The following code is only a portion of the whole. Please forgive me for using gets and for declaring variables not used in this portion. There are also some "stupid" parts, but they will be changed after the code works as it should :) Could you please help me debug this if statement of line 58? (You will see the comment next to it).

Here is the code:

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

char *colour(char *xr, int N);
int RandomInteger(int low, int high);

int main()
{
    int i,j,q,N,w,z,k,A[6][4],win;
    char *xr,*xrx,temp[1],sur[]="SURRENDER";

    printf("Gimme number from 1-100");
    scanf("%d",&N);
    getchar();

    for(i=0; i<6; i++) A[i][1]=0;
    for(i=0; i<6; i++) A[i][2]=0;
    for(i=0; i<6; i++) A[i][3]=0;
    A[0][0]=87,A[1][0]=66,A[2][0]=71,A[3][0]=89,A[4][0]=80,A[5][0]=82;
    xr=malloc(N*sizeof(char));
    xrx=malloc(N*sizeof(char));
    xr=colour(xr,N);

    printf("\nxr: %s",xr);
    i=0;
    q=0;
    z=1;
    printf("\nGimme the color sequence: ");
    gets(xrx);
    //if(strcmp(xrx,sur)==0) goto end;

    while(xrx[i])
    {
   if(xrx[i]!=87 && xrx[i]!=66 && xrx[i]!=71 && xrx[i]!=89 && xrx[i]!=80 && xrx[i]!=82)               
       {z=0;}
       if(z==0) 
       {
           printf("\nGimme the color sequence: ");
           gets(xrx);
           i=0; 
           z=1;
       }
       else i++;
    }

    i=k=q=0;
    while(xr[i])
    {
    if(xr[i]==xrx[i]) 
    {
            q++;
            for(w=0; w<=5; w++)
            {
                     if(xr[i]==A[w][0]) //SOMETIMES IT DOESN'T WORK
                     {
                             printf("\nhere:");
                             A[w][3]=1;
                             printf("%d",A[w][3]);
                             break;
                     }
            } 
    }
    i++;
    }
    printf("\nColor and position correct: %d",q);
    for(i=0; i<=5; i++) printf("\n%d",A[i][3]); //PERIERGO


   // end:
   printf("!!BYE!!");
   return 0;
}

char *colour(char *xr, int N)
{
    int r,i,j,number;
    char *str,temp[2];

    str=calloc(N,sizeof(char));
    srand((int)time(NULL));
    for(j=0; j<N; j++)
    {
       r=RandomInteger(0,5);
       if(r==0)
       {
           temp[0]='W';
           temp[1]='\0';
           strcat(str,temp);
       }
       else if(r==1)
       {
       temp[0]='B';
       temp[1]='\0';
       strcat(str,temp);
       }
       else if(r==2)
       {
           temp[0]='G';
           temp[1]='\0';
           strcat(str,temp);
       }
       else if(r==3)
       {
           temp[0]='Y';
           temp[1]='\0';
           strcat(str,temp);
       }
       else if(r==4)
       {
           temp[0]='P';
           temp[1]='\0';
           strcat(str,temp);
       }
       else if(r==5)
       {
           temp[0]='R';
           temp[1]='\0';
           strcat(str,temp);
       }
    }
    return str;
}

int RandomInteger(int low, int high)
{
    int k;
    double d;
    d=(double)rand()/((double)RAND_MAX+1);
    k=(int)(d*(high-low+1));
    return (low+k);
}

Answer 1

This is accessing beyond the bounds of the array, causing undefined behaviour:

for(i=0; i<5; i++) A[i][3]=0;

as A has dimensions [5][3]. Array indexes run from 0 to N - 1 where N is the number of elements in the array. There other occurrences of out of bounds accesses:

A[5][0]=82;

and within function color():

char *str,temp[1];
str=malloc(N*sizeof(char)); /*Note sizeof(char) is guaranteed to be 1: omit.*/

/* snip */
temp[1]='\0';

str needs to be larger by one (unsure why temp even exists).

Instead of looping to set all elements in array A to zeroes use an aggregate initializer:

int A[5][3] = { { 0 } };

See Why is the gets function so dangerous that it should not be used?