Question

I have code to dynamically allocate an array of 100 doubles to a pointer and initialize the memory with values from 1.0 to 100.0.

My question is, in the code below why don’t I have to write *ptr++ at each iteration of the for loop. I’ve tried it and it doesn’t work.

void allocate_array(){
    double *ptr;
    ptr= (double*)malloc(sizeof(double)*100);
    int i=0;
    float j=0.0;
    for(i=0;i<100;i++){
        *ptr=j++;
        printf(" %0.1lf\n",*ptr);
    }
}

Answer 1

Well, you don’t have to do anything. In your code, you don’t initialize the whole array – you just assign 100 different values to its first member. Your code is just like:

double d;
for(i=0;i<100;i++){
            d=j++;
            printf(" %0.1lf\n",d);
}

If you want to initialize the whole array, do something like:

double *temp=ptr;
for(i=0;i<100;i++){
            *temp=j++;
            printf(" %0.1lf\n",*temp++);
}