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Need help with c programming array question :)?

• Thanks for checking out my question :) So, the question goes like this: Write a program, addarrays.c, which reads two arrays x1 and x2 from the file addarrays.in, computes their sum and writes the sum to the file addarrays.out. In more detail main carrys out the following steps: open the two files addarrays.in and addarrays.out. read the array size, n, from the file. allocate the two arrays x1 and x2 read the values from the file into the two arrays call the function add which creates a new array, y, that is the sum of the two arrays x1 and x2 write the array size followed by sum, y, to the file addarrays.out. Array size allocation has to be done dynamically. ______________________________________… And here is my solution: #include <stdio.h> #include <stdlib.h> void add(float *x1,float *x2,float *y,int *n); int main(void) { float* x1; float* x2; float *y; /* the sum of x1 and x2 */ int n; /* the size of the arrays */ int i=0; float sum; FILE *fin = fopen("addarrays.in","r"); FILE *fout = fopen("addarrays.out","w"); fscanf(fin,"%d",&n); x1 = (float*) malloc(n*sizeof(float)); x2 = (float*) malloc(n*sizeof(float)); for(i=0;i<n;i++) { fscanf(fin,"%f%f",&x1[i],&x2[i]); } add(x1,x2,y,&n); fprintf(fout,"%d\n",n); for(i=0;i<n;i++) { //fprintf(fout,"%f\n",x1[i]); fprintf(fout,"%f\n",y[i]); } fclose(fin); fclose(fout); system("pause"); return 0; } void add(float *x1,float *x2,float *y,int *n) { int i; y = (float*) malloc((*n)*sizeof(float)); for(i=0;i<*n;i++) { y[i] = x1[i]+x2[i]; } } ______________________________________… The program just crashes :( Any help is appreciated :)

• Answer:

  The problem is that the output array is allocated in the "add()" method, but is NOT returned to the calling method. In order to change your program as little as possible, I just turned it into a reference parameter. #include <stdio.h> #include <stdlib.h> void add (float *x1, float *x2, float **y, int *n); int main (void) {   float *x1;   float *x2;   float *y; /* the sum of x1 and x2 */   int n; /* the size of the arrays */   int i = 0;   float sum;   FILE *fin = fopen ("addarrays.in", "r");   FILE *fout = fopen ("addarrays.out", "w");   fscanf (fin, "%d", &n);   x1 = (float *) malloc (n * sizeof (float));   x2 = (float *) malloc (n * sizeof (float));   for (i = 0; i < n; i++) {     fscanf (fin, "%f%f", &x1[i], &x2[i]);   }   add (x1, x2, &y, &n);   fprintf (fout, "%d\n", n);   for (i = 0; i < n; i++) {     //fprintf(fout,"%f\n",x1[i]);     fprintf (fout, "%f\n", y[i]);   }   fclose (fin);   fclose (fout);   // system ("pause");   return 0; } void add(float *x1, float *x2, float **y, int *n) {   int i;   *y =  (float *) malloc ((*n) * sizeof (float));   for (i = 0; i < *n; i++) {     (*y)[i] = x1[i] + x2[i];   } }