创建一个程序，将两个数字以相等的间隔相除

Question

I made the first part of the program, but I don't understand the part of dynamic memory allocation and calculation using pointers. What should I coding? The contents of the program.

1. Consider creating a sequence of numbers by dividing the two numbers at equal intervals. For example, if you want to create 5 numbers that are evenly spaced from 0.0 to 2.0, you can divide the interval from 0 to 2 into 4 equal parts (considering the value at the end) and arrange the numbers every 0.5. It becomes 0.0, 0.5, 1.0, 1.5, 2.0.
2. Then, when you enter the first number, the last number, and the total number of values, an array containing the values ​​at equal intervals from the "first number" to the "last number" is created by dynamic memory allocation, and each value is created. After displaying, create a program (see execution example) that also displays the square of each value.
3. The "first number" and "last number" are floating-point numbers, and the "total number of values" is an integer. The memory allocated by dynamic memory allocation should be the minimum required according to the "total number of values". Display each value At the first display, output the value stored in the array as it is.

my source code

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

    
    int main ()
    {
       int num, i;
       double dfirst, dlast;
       double * x;
    
       / * Enter the first value, the last value, and the number to divide * /
       printf ("Input first, last, total number of x []:");
       scanf ("% lf% lf% d", & dfirst, & dlast, & num);
    
       / * Create after this * /
    
       / * Allocate memory * /
    
      / * Determine the value to store.
         Be careful not to divide by an integer and decide the number of divisions in consideration of the end value * /
    
       / * Display results * /
    
       / * Post-processing * /
       return 0;
    }

Execution result want to do

% ./a.out
Input first, last, total number of x[]: 0.0  2.0  5
Values of x
0.000 0.500 1.000 1.500 2.000
Values of x^2
0.000 0.250 1.000 2.250 4.000
% ./a.out
Input first, last, total number of x[]: 1.0  2.0  11
Values of x
1.000 1.100 1.200 1.300 1.400 1.500 1.600 1.700 1.800 1.900 2.000
Values of x^2
1.000 1.210 1.440 1.690 1.960 2.250 2.560 2.890 3.240 3.610 4.000

Answer 1

In C you allocate memory dynamically with the function malloc . This function is quite low-level and the programmer must be very careful to specify the right size of the requested memory. To make the function easier to use it can be convenient to define a macro which also provides error handling:

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

#define NEW_ARRAY(ptr, n) \
    (ptr) = malloc((n) * sizeof (ptr)[0]); \
    if ((ptr) == NULL) { \
        fprintf(stderr, "Memory allocation failed: %s\n", strerror(errno)); \
        exit(EXIT_FAILURE); \
    }

With the macro function in place, you can simply add

NEW_ARRAY(x, num);

to your program to allocate an array x of num elements. When you are done with x you free the memory with free ( x ). In your program you also need to check the result from scanf to make sure the input is valid. Good luck!