cmd command line into DOS mode compile Run C language program implement string conversion

Requirement: Enter a string (less than 50 in length), then filter out all non-numeric characters, get a string of numeric characters and convert it to a double result output (4 decimal places).

SOURCE program:

#include <stdio.h>
int change (Char*source,char *des)
{
int i=0;
while (*source)
{
if (*source>= ' 0 ' &&*source<= ' 9 ')
Des[i++]=*source;
source++;
}
des[i]= ' + ';
return i;
}
Double Calcu (char*s)
{Double result=0;
while (*s)
{
result=result*10+ (*s-48);
s++;
}
return result;
}
int main ()
{
Char str[50],strdes[50];
Gets (str);
if (change (str,strdes))
{
printf ("%.4f\n", Calcu (Strdes));
}
Else
printf ("The digital string is empty!");
return 0;
}

Realize:

cmd command line into DOS mode compile Run C language program implement string conversion