Question

After debugging i get this error message : HEAP CORRUPTION DETECTED after normal block (#55). If I increse the size of the array (no_of_days+1), it’s working, but i don’t know if it’s right.
What i am doing wrong?

int main()
{

    int no_of_days=0;
    int no_operations=0;
    int *a;
    int i;
    FILE *pfile1=NULL;
    FILE *pfile2=NULL;
    char *filename1="input.txt";
    char *filename2="output.txt";

    pfile1=fopen(filename1, "r");
    if(pfile1==NULL)
    {
        printf("Error on opening the file %s.",filename1);
        return 0;
    }
    fscanf(pfile1,"%d%d",&no_of_days,&no_operations);
    a=(int*)malloc((no_of_days)*sizeof(int));
    if(a==NULL)
    {
        printf("Memory allocation failed.");
        return 0;
    }
    for(i=1;i<=no_of_days;i++)
    {
        fscanf(pfile1,"%d",&a[i]);
    }
    pfile2=fopen(filename2,"a");
    if(pfile2==NULL)
    {
        printf("Memory allocation failed!",filename2);
    }
    for(i=1;i<=no_of_days;i++)
    {
        fprintf(pfile2,"%d",a[i]);
    }
    free(a);
    fclose(pfile1);
    fclose(pfile2);

Answer 1

a=(int*)malloc((no_of_days)*sizeof(int));
/* ... */
for(i=1;i<=no_of_days;i++)

Indexing starts from 0 so accessing a[no_of_days] is illegal. Change that for line to:

for(i = 0; i < no_of_days; i++)