Interactive execution of binary commands, and C/C++ expressions, statements, functions, 
and programs in a Ch command window are portable across different platforms.

The interactive execution below illustrates how different conversion specifiers
in a format string affect the output.

    > 2*3+4
    10
    > int i = 16
    > double f = 12.3456
    > sizeof(int)
    4
    > sizeof(i)
    4
    > sizeof(double)
    8
    > sizeof(f)
    8
    > i
    16
    > 2*i
    32
    > printf("%d", i)
    10
    > printf("%5d", i)      // field width 5
       10 
    > printf("%#d", i)
    10
    > printf("%#x", i)
    0xa
    > printf("%#X", i)
    0XA
    > printf("%x", i)
    a
    > printf("%X", i)
    A
    > printf("%o", i)
    12
    > printf("%b", i)
    1010
    > printf("%f", f)
    12.345600
    > printf("%lf", f)
    12.345600
    > printf("%.2lf", f)   // precision with 2 digits after decimal point
    12.35
    > printf("%8.2lf", f)  // field with of 8
       12.35
    > printf("%d", f)      // a common mistake using %d for floating-point numbers
    2075328197
    > printf("%f", i)      // a common mistake using %f for integers
    0.000000
    > 


The interactive execution below illustrates a difficult concept 
how pointers in C are related to the memory they point to. 

    > int i, *p, **p2     // i is an integer, p pointer, p2 double pointer
    > i=10                // i is assigned value 10
    10
    > p=&i                // p points to address of i
    00D847C0
    > *p                  // the memory pointed by p has value 10 
    10
    > p2=&p               // p2 points to address of p
    00D84D30
    > **p2                // the memory pointed by the pointer at p2 has value 10
    10
    >


Commands below illustrate a difficult concept that an array name is a pointer, 
whereas a pointer can also be treatd as an array.

    > int a[5]={1,2,3,4,5}, *p
    > p= &a[2]
    009BD3D8
    > a[2]
    3
    > *(a+2)
    3
    > *p
    3
    > p[0]
    3
    > p[1]
    4
    >


Commands below illustrate how struct can be handled interactively. 
Note that because of alignment, the size of structure tag is 16, not 12.

    > struct tag {int i; double d;} s
    > s.i =20
    20
    > s.d=30
    30.0000
    > s
    .i = 20
    .d = 30.0000
    > sizeof(struct tag)
    16      
    > 

Not only C statements and expressions, but also C functions and  programs,
can be interactively executed in Ch.  All functions in the C standard libraries 
can be executed interactively and can be used inside user defined functions.
For example, 

    > srand(time(NULL))
    > rand()
    4497
    > rand()
    11439
    > double add(double a, double b) {double c; return a+b+sqrt(2);}
    > double c
    > c = add(10.0, 20)
    31.4142

After the random number generator is seeded with a time value 
in srand(time(NULL), the function rand() is called to generate 
two random numbers. The function add() which calls the mathematical 
function sqrt() is defined at the prompt and then used.

Commands below demonstrates how Ch can be used as a calculator for
scientific numerical computing and visualization.