C functions - useful prepackaged modules for programmer

In the CSCI1110, chapter 7 –function was taught from week 7 to week 8. This is one of the key topics in the curriculum of CSCI1110. Now let me summarize what I have learnt from chapter 7 –function.

Part 1

1.1 Contents of the lectures

In chapter 7, I have learnt some fundamental concepts about C functions. What are C functions? Modules in C are called functions. C programs are typically written by combining new functions you write with prepackaged functions available in the C standard library. The C standard library provides a rich collection of functions for performing common mathematical calculations, string manipulations, character manipulations, inputs/outputs, and many other useful operations. This makes the design of the program easier since these functions provide many of the capabilities programmer needs. Therefore, it is very important for a good programmer to acquire a good skill of using C functions. In chapter 7, the knowledge of C functions I had learnt include (1) function definitions, (2) function prototypes, (3) pre-defined function.

(1)   Function definitions :

• The general format for a function definition is

       Return-value-type function-name( parameter-list)

        {

                Definitions

                Statements

        }

• The return-value-type states the type of the value returned to the calling function. If a function does not return a value, the return-value-type is declared as void.

• The function-name is any valid identifier.

• The parameter-list is a comma-separated list containing the definitions of the variables that will be passed to the function. If a function dose not receive any value, parameter-list is declared as void.

• The function body is the set of definitions and statements that constitute the function.

• The arguments passed to a function should match in number, type and order with the parameters in the function definition.

• When a program encounter a function call, control is transferred from the point of invocation to the called function, the statements of the called function are executed and control returns to the caller.

• A called function can return control to the caller in one of three ways. If the function does not return a value, control is returned when the function-ending right brace is reached, or by executing the statement return ;

 If the function does return a value, the statement return    

 expression; returns the value of expression.

 

(2)   Function Prototypes :

• A function prototype declares the function’s return type and declares the number, types, and order of the parameters the function expects to receive.

• Function prototype enables the compiler to verify the functions are called correctly.

• The compiler ignores variable names mentioned in the function prototype.

• Argument in a mixed-type expression are converted to the same type via the C standard’s usual arithmetic conversion rules.

(3)   Pre-defined function :

• C provides many built-in functions. To call them, we have to know the following info (which can be found from manuals): name, functionality, parameters, return value

• You also need to know which header file(s) to include. E.g. 

        - To use printf(…), you have to include "stdio.h" as

     #include <stdio.h>

   -To use math functions, you have to include "math.h" as

     #include <math.h>

More about C function : 

Website :
http://www2.its.strath.ac.uk/courses/c/section3_9.html

Video:

1.2 Learning Process:

In order to understand the principle of C functions and acquire the techniques of using different functions for performing useful operations, I use different methods to let myself to understand the principle and uses of the techniques during the learning process.

(1)   To understand the principle of C functions in the view of   

        worker-function relationship

The principle of C functions is that, functions are invoked by a function call, which specifies the function name and provides information (as arguments) that the function needs to perform its designated task.

However, this concept is quite abstract and difficult to understand.

In order to understand the principle of C functions clearly, I regard the relationship between the caller and the called function as a worker-function relationship :

A boss (the caller) asks a worker (the called function) to perform a task and report back when the task is done. For example, a function needing to display information on the screen calls the worker function printf to perform that task, then printf display information and reports back – or returns – to the caller when its task is completed. The boss function does not know how the worker functions, and the boss will be unware of this.

Figure showing a boss function communicating with several worker functions in a hierarchical manner.

(2)  Record the common programming error in using C functions.

Since the use of C functions is complex, we may make some programming errors easily in using C function. In acquire the techniques of using different functions for performing useful operations accurately without mistakes or errors, I recorded the common programming error in using C functions and some error-prevention skills during the learning process.

• Specifying function parameters of the same type as double x,y instead of double x, double y results in a compilation error.
• Placing a semicolon after the right parenthesis enclosing the parameter list of a function definition is a syntax error.
• Defining a parameter again as a local variable in a function is a compilation error.
• Defining a function inside another function is a syntax error.
• Forgetting the semicolon at the end of a function prototype is a syntax error.
• Converting from a higher data type in the promotion hierarchy to a lower type can change the data value. Many compilers issue warnings in such cases. 

Part 2

2.1 A interesting topic in the lesson – math library function in C program

A brief description about the math library function in C program :

  
C mathematical operations are a group of functions in the standard library of the C programming language implementing basic mathematical functions.



Math library functions allow programmer to perform certain common mathematical calculations. It is normally used in a program by writing the name of the function followed by left parenthesis followed by the argument of the function followed by a right parenthesis.

Most of the mathematical functions are placed in math.h header (cmath header in C++). 
The functions that operate on integers, such as abs, labs, div, and ldiv, are instead specified in the stdlib.h header (cstdlib header in C++).
Any functions that operate on angles use radians as the unit of angle.

More about C math library :

 

2.2 My opinion, commends, ideas, and further information about math library function in C program

I think Math library function in C program is a very useful tool for solving mathematics or engineering problem in real world. By calling the Math library function in C program, we can perform some complex mathematics calculation or solve some difficult mathematics problem in an easier way.

In the below, there are some advanced examples about use of Math library function that are not included in the lecture.

For example, we can use log2( ) function to convert numbers in the base 10 to the base 2 easily.

#include <math.h>
#include <stdio.h>
  int main(void)
  {
    double val = 1.0;     do {
      printf("%f %f\n", val, log2(val));
      val++;
    } while (val<11.0);     return 0;
  }

For the above C program using log2( ) function in the Math library, the following result can be obtained.

Apart from it, the Math library function in C program can also perform more complex mathematics calculation. For example, we may use it to create a matrix, which is commonly used in solving engineering problems.

To create a sparse matrix froma standard numeric array, we may use the mlfSparse()

routine. mlfSparse() converts the numeric array into sparse storage format.

#include <math.h>
#include <stdio.h>
  int main(void)
  {

static double row_subscripts[] = { 3, 4, 5, 4, 5, 6 };

static double col_subscripts[] = { 4, 3, 3, 5, 5, 4 };

mxArray *i = NULL;

mxArray *j = NULL;

mxArray *S = NULL;

mlfAssign(&i, mlfDoubleMatrix(1, 6, row_subscripts, NULL));

mlfAssign(&j, mlfDoubleMatrix(1, 6, col_subscripts, NULL));

mlfAssign(&S, mlfSparse(i, /* Row subscripts */

j, /* Column subscripts */

mlfScalar(9), /* Data */

mlfScalar(8),

mlfScalar(7),

NULL));

mlfPrintMatrix(S);

mlfPrintMatrix(mlfFull(S));

mxDestroyArray(i);

mxDestroyArray(j);

mxDestroyArray(S);

    return 0;
  }

For the above C program using mlfSparse(C math library reference), the following result can be obtained.

In fact, the C Math Library is commonly used as a component in different mathematics or engineering softwares.Fr example, the C Math Library is a component of the MATLAB Compiler. The MATLAB Compiler includes the Compiler, the C Math Library and the Graphics Library. The Math library provides the core math and data analysis routines from MATLAB in object library form. We can use the Math library with the MATLAB Compiler to create math functions based on MATLAB in your external applications ,or embed the Math library in standalone applications.

From these examples, we can see that Math library function is a very useful function in C program. It helps engineer to solve difficult and complex engineering mathematics problem in the real applications. As a engineering student, I must acquire  the techniques of using this function for solving engineering problems.

More about C mathematical function :
http://en.wikipedia.org/wiki/C_mathematical_functions

In the coming lecture, I will learn more advanced knowledge about C program. I will continue to make effort on writing C program and hope that I can acquire a good skill of writing C program at the end of this semester.