01. C programming language

As seen before C programming language is:

• low-level (calculational model is equal to hardware);
• procedural algorithmic (has classical control flow, data types, variables, function calls etc.)

C program structure

• All code is formed by functions

  • Function is subroutine with a number of arguments (incl. none) and return value (can be void)

  • A program must contain main() function

    • main() is called from outside (so called «C runtime»), and returned an int value back to C runtime

    • main() accepts two arguments (integer and array of strings, see later); in many systems they corresponds program command line arguments

• All data is described by variables.

  • Variable is labeled peace of memory corresponding data of certain type; the amount of memory variable has consumed is always fixed and corresponds its type

  • Variables must be provisionally defined
  • Variable can be:

    • global:

      • defined (almost always) between functions,

      • placed statically in data memory segment,
      • accessible (visible by name) from any part of the program,
      • exists all along the program runs;

    • local:

      • defined inside a function,

      • placed dynamically in stack,
      • accessible only from the function interior,
      • lose it's value when function function call is finished;

    • register:

      • defined inside a function,

      • placed dynamically in CPU registers when applicable, otherwise in stack
      • accessible only from the function interior,
      • lose it's value when function function call is finished;
• Data type can be:
  • Scalar: integers of various size/signness and floats with various size

  • Pointer: address of certain type data or function; all pointers have one size

  • Structure: a fixed number of data pieces of several types, in a declared order, treated as one memory chunk
• Function control flow contents:
  • Expressions
  • Conditionals
  • Circles
  • Switches
  • Returns
• All code is transformed by preprocessor
  • To include other source files (mainly macros and library declarations)

  • To expand macros

• C preprocessor
  • has parametric macros
  • has preprocessor-time conditionals
  • has preprocessor-time expressions

C program example

   1 #include <stdio.h>
   2 #define START 100500
   3 
   4 int num=START;
   5 float flt=2.718281828459045;
   6 
   7 int main(int argc, char *argv[]) {
   8         int i;
   9         register int j;
  10 
  11         printf("Enter a cardinal: ");
  12         scanf("%d", &num);
  13 
  14         flt = 0.0;
  15         for(i=1; i<num; i++)
  16             for(j=1; j<i; j++)
  17                 flt += 1./j;
  18 
  19         printf("Result is %f\n", flt);
  20         return 0;
  21 }

H/W