LAIB 8 Exercise 1: Magic square

laib8ex1.c

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

int rs[]={1,0,0,0},cs[]={0,1,0,0},rc[]={0,1,1,1},cc[]={1,0,1,-1};

int magic_r(int **magic_square,int n,int row,int col,int target_sum,int *marked,int n_elements){
    int i,j,k,sum,under=1,wrong;
    for(i=1;i<=n_elements&&under;i++){
        if(!marked[i-1]){
            magic_square[row][col]=i;
            marked[i-1]=1;

            wrong=0;
            for(j=0;j<4;j++) {
                sum=0;
                for (k = 0; k < n; k++)sum += magic_square[rs[j] * row + rc[j] * k][(cc[j]<0?n-1:0) + cs[j] * col + cc[j] * k];
                if(sum>target_sum)under=0;
                if(sum!=target_sum&&((j==0&&col==n-1)||(j==1&&row==n-1)||(j==2&&col==n-1&&row==n-1)||(j==3&&row==n-1)))wrong=1;
            }
            //printf("\n\nR%d C%d U%d W%d\n",row,col,under,wrong);for (k = 0; k < n; k++) { for (j = 0; j < n; j++)printf("%d ", magic_square[k][j]);printf("\n"); }
            if(under&&!wrong){
                if(col == n - 1 && row == n - 1)return 1;
                if(magic_r(magic_square,n,col+1<n?row:row+1,col+1<n?col+1:0,target_sum,marked,n_elements))return 1;
            }
            magic_square[row][col]=0;
            marked[i-1]=0;
        }
    }
    return 0;
}

int **doMagic(int n){
    int i,j,sum=0, **magic_square;
    int n_elements=n*n;
    for(i=1;i<=n_elements;i++)sum+=i;
    int *marked=(int*)malloc(sizeof(int)*n*n);
    if(marked==NULL)return NULL;
    for(i=0;i<n_elements;i++)marked[i]=0;
    magic_square=(int**)malloc(sizeof(int*)*n);
    if(magic_square==NULL){printf("ERROR: memory allocation magic_square.\n");return NULL;}
    for(i=0;i<n;i++){
        magic_square[i]=(int*)malloc(sizeof(int)*n);
        if(magic_square[i]==NULL){printf("ERROR: memory allocation magic_square.\n");return NULL;}
    }
    for(i=0;i<n;i++)for(j=0;j<n;j++)magic_square[i][j]=0;
    if(magic_r(magic_square, n, 0, 0, sum/n, marked, n_elements)){
        free(marked);
        return magic_square;
    }
    else{
        free(marked);
        for(i=0;i<n;i++)free(magic_square[i]);
        free(magic_square);
        return NULL;
    }
}

int main(int argc,char **argv){
    FILE *output;
    int **magic_square,n,i,j;

    if(argc<3){
        printf("ERROR: Wrong number of arguments! An integer and a file name needed.\n");
        return EXIT_FAILURE;
    }

    n=atoi(argv[1]);
    if(n==0)return EXIT_FAILURE;

    output=fopen(argv[2],"w");
    if(output==NULL){
        printf("ERROR: Can't open %s.\n",argv[2]);
        return EXIT_FAILURE;
    }

    magic_square=doMagic(n);
    if(magic_square==NULL){
        printf("ERROR: Something bad happened while doing magic.\n");
        return EXIT_FAILURE;
    }else{
        for (i = 0; i < n; i++) {
            for (j = 0; j < n; j++)fprintf(output, "%d ", magic_square[i][j]);
            fprintf(output, "\n");
        }
    }

    fclose(output);

    for(i=0;i<n;i++)free(magic_square[i]);
    free(magic_square);

    return 0;
}