Computers and programming

The 5th lecture

Jiří Šebesta

TOPIC

1. Functions - introduction2. Headers of functions 3. Recursion of functions4. Libraries of functions5. Example

Functions – introduction (1/3)

• Function: a sequence of statements completed by a header

• Application:– repetitively executed sequence of statements– structuring a program– events handling

Functions – introduction (2/3)

• What is happen, if the function is called ?

Functions – introduction (3/3)

• The basic types of functions:- functions without parameter

- functions with parameter- call by value (it do not change the content of an input variable, which is declared in the superior code)- call by reference (a pointer is hand in function as a parameter, the content of input parameter can be changed)

- function with/without returning value

Headers of functions (1/13)

void func_name(void){ }

void warning(void) // no input, no output{ printf("Your computer is being destroyed"); getchar();}

void main(void){ warning(); // calling the function}

• A function without a parameter and without a returning value:

Headers of functions (2/13)

double func_name(double A){ }int pow3(int A) // 1 input, 1 output{ int y = A*A*A; return y;}

• A function with one parameter called as a value and with a returning value:

void main(void){ int n; for(n=0; n<20; n++) printf(“%d^3 is %d\n“, n, pow3(n));}

Headers of functions (3/13)

double func_name(double A, double B) { }

float pow_n(float A, int B) // 2 inputs, 1 output{ float y = 1; int n;

for(n=0; n<=B; n++) if(n>0)

y *= A; return y;}

• A function with two parameters called as values and with a returning value:

The function for n-power of rational number

Headers of functions (4/13)

int main(void){ int n; float y[9]; float m = 5.123; for(n=2; n<11; n++) { y[n-2] = pow_n(m, n); printf("%dth power of %f is %f\n", n, m ,y[n-2]); } getchar(); return 0;}

Source code: Ex51.c

Headers of functions (5/13)

??? func_name(char* A) { }

int numinstr(char *s){ int n, count=0;

for(n=0; s[n]!='\0'; n++) if(s[n]>='0'&&s[n]<='9')

count++;

return count ;}

• A function with a parameter as a string

The function returning number of ciphers in the string

Headers of functions (6/13)

int main(void){ char txt1[] = "ab9bj65D9"; char txt2[] = "34x9z56A0"; char txt3[] = "3cvz1111E";

int n1, n2, n3;

n1 = numinstr(txt1); n2 = numinstr(txt2); n3 = numinstr(txt3); printf("%d in 1st, %d in 2nd, %d in 3rd", n1, n2, n3); getchar(); return 0;}

Source code: Ex52.c

Headers of functions (7/13)

??? func_name(int *A, int *B) { }

void polar2cart(float *A, float *B) // A is magnitude{ // B is phase in deg. float pha;

pha = 3.1415 * *B/180; *B = *A * sin(pha); // B is imag. part *A = *A * cos(pha); // A is real part }

• A function with parameters called as reference

• Parameters are pointers

The function for conversion from polar to Cartesian coordinates

Headers of functions (8/13)

int main(void){ float x=2.0; float y=90.0;

printf("Magnitude is %f and phase is %f deg.", x, y);

polar2cart(&x, &y); printf("Real part is %f and imag. part is %f", x, y);

getchar(); return 0;}

Source code: Ex53.c

Headers of functions (9/13)

float mean(float *vect, int n) // vect is input vector{ // n is length of the vector int m, float s=0; // s is partial sum for(m=0; m<n; m++) // for all elements of vector

s += vect[m];

return s/(1.0*n); // average computation }

• A function with parameter, which references the pointer to the first element of array (alike for strings)

The function for mean value calculation from vector of rational numbers

Headers of functions (10/13)

int main(void){ float x[5], m; int len_x=5, n;

srand(time(NULL)); for(n=0; n<len_x; n++) {

x[n]=(rand()%1000)/100.0;printf("%4.2f\n", x[n]);

} m = mean(x, len_x); printf("The average of vector of number is %f", m); getchar(); return 0;}

Source code: Ex54.c

Headers of functions (11/13)

typedef int t_mat[3][3] ;

void func_name(t_mat A, t_mat B) { }

• Own type of variable can be defined by using typedef

int func_name(t_mat A) { }

t_mat func_name(t_mat A) { }

!!! A function can return a value or pointer only (no array) !!!

Headers of functions (12/13)

typedef int t_mat[3][3];int det_mat(t_mat A) // determinant of 3x3 matrix { int det=0, m, n, pplus, pminus; for(m=0; m<3; m++) {

pplus=1; pminus=1;for (n=0; n<3; n++){ pplus*=A[(m+n)%3][n]; pminus*=A[(m+n)%3][2-n];

}det+=pplus-pminus;

} return det; }

The function for determinant calculation from matrix 3 by 3

Headers of functions (13/13)

int main(void){ t_mat mat; int m, n; srand(time(NULL)); for(m=0; m<3; m++) for(n=0; n<3; n++)

mat[m][n]=rand()%198-99; printf("The determinant is %d", det_mat(mat));

getchar(); return 0;}

Source code: Ex55.c

Recursion of function (1/1)

unsigned int factorial(unsigned int n){ if(n) // test if n is not zero return n*factorial(n-1); // n is not zero else // n is zero return 1;}

int func_name(int A) {…

x = func_name(y);

…}

• A function can call the same function in its body

Source code: Ex56.c

The function for factorial computation

Libraries of functions (1/10)

• my_lib.c: a file containing source codes of our functions

• my_lib.h: a file containing headers of our functions from the same-name file

• #include ”my_lib.h”: have to be inserted in our program, in which functions form the library file my_lib.c are called

• A library can be build-up using own set of functions:

Libraries of functions (2/10)

• In Code::Blocks: File > New > File

• my_lib.c + my_lib.h into the directory of the project or specific own directory for own libraries

Libraries of functions (3/10)

• Setting of paths for compiler in Code::Blocks:

Settings > Compiler

• add paths with sources and headers

Libraries of functions (4/10)

• Own library of functions for operations with 3 by 3 matrixes

• header file matops.h

typedef int t_mat[3][3];int det_mat(t_mat A); // determinant of Avoid print_mat(t_mat A); // printing A void gen_mat(t_mat A, int start, int stop); // gener. Avoid copy_mat(t_mat A, t_mat B); // copying A to Bvoid add_mat(t_mat A, t_mat B); // A=A+Bvoid sub_mat(t_mat A, t_mat B); // A=A-Bvoid clr_mat(t_mat A); // zeroizing A

• own types of variables definitions• header functions with definitions of types for all input and output parameters

Libraries of functions (5/10)

• source codes of library matops.c

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

typedef int t_mat[3][3];

int det_mat(t_mat A) // compute determinant{ int det=0, m, n, pplus, pminus;

for(m=0; m<3; m++){

• it includes source codes for all functions according to header file matops.h

Libraries of functions (6/10)

pplus=1; pminus=1;for (n=0; n<3; n++){

pplus*=A[(m+n)%3][n];pminus*=A[(m+n)%3][2-n];

}det+=pplus-pminus;

} return det; }

Libraries of functions (7/10)

void print_mat(t_mat A) // printing matrix A{ int m,n;

for(m=0; m<3; m++){ for(n=0; n<3; n++)

{printf("%4d ", A[m][n]);

}printf("\n");

}} void gen_mat(t_mat A, int start, int stop) // random{ int m, n; // generation of matrix A srand(time(NULL));

for(m=0; m<3; m++)for(n=0; n<3; n++)

A[m][n]=rand()%(stop-start+1)+start;}

Libraries of functions (8/10)

void copy_mat(t_mat A, t_mat B) // copying A to B{

int m, n; for(m=0; m<3; m++)

for(n=0; n<3; n++)A[m][n]=B[m][n];

}

void add_mat(t_mat A, t_mat B) // A=A+B{

int m, n; for(m=0; m<3; m++)

for(n=0; n<3; n++)A[m][n]+=B[m][n];

}

Libraries of functions (9/10)

void sub_mat(t_mat A, t_mat B) // A=A-B{

int m, n;for(m=0; m<3; m++)

for(n=0; n<3; n++)A[m][n]-=B[m][n];

}

void clr_mat(t_mat A) // zeroizing A{

int m,n;for(m=0; m<3; m++)

for(n=0; n<3; n++)A[m][n]=0;

}

Libraries of functions (10/10)

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

t_mat mat1, mat2, mat3; // this type was defined //in mathops.h

int m, n; gen_mat(mat1, -9, 9);

print_mat(mat1);printf("The det. of mat1 is %d\n",det_mat(mat1));copy_mat(mat3, mat1);sub_mat(mat1, mat2);…

• Example of a program, which uses own library matops.h

Source code: Ex57.c + matops.c(h)

Example (1/2)

Create a library with functions for computing areas of 2-D geometric objects (build-up functions for

rectangle, ellipse and triangle).

baSr baSe baSt 5.0

double s_rect(double a, double b);double s_ell (double a, double b); double s_tri (double a, double b);

• Header file for library areas2D.h

Example (2/2)

baSr

baSe

baSt 5.0

#include "areas2D.h"

double s_rect(double a, double b){ return a*b;}

double s_ell (double a, double b){ return 3.1415*a*b;}

double s_tri (double a, double b)

{ return 0.5*a*b;}

• Library functions in areas2D.cpp

Source code: Ex58.c + areas2D.c(h)

TOPIC OF THE NEXT LECTURE

Advanced data types

THANK YOU FOR YOUR ATTENTION