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The 5 th lecture Jiří Šebesta

Computers and programming. The 5 th lecture Jiří Šebesta. TOPIC. Functions - introduction Headers of functions Recursion of functions Libraries of functions Example. Functions – introduction (1/3). Application: repetitively executed sequence of statements structuring a program

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The 5 th lecture Jiří Šebesta

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  1. Computers and programming The5th lecture Jiří Šebesta

  2. TOPIC Functions - introduction Headers of functions Recursion of functions Libraries of functions Example

  3. Functions – introduction (1/3) • Application: • repetitively executed sequence of statements • structuring a program • events handling Function:a sequence of statements completed by a header

  4. Functions – introduction (2/3) What is happen, if the function is called ?

  5. 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

  6. A function without a parameter and without a returning value: Headers of functions (1/13) void func_name(void){ } voidwarning(void) // no input, no output { printf("Your computer is beingdestroyed"); getchar(); } void main(void) { warning(); // calling the function }

  7. A function with one parameter called as a value and with a returning value: Headers of functions (2/13) double func_name(double A){ } intpow3(int A) // 1 input, 1 output { int y = A*A*A; return y; } void main(void) { int n; for(n=0; n<20; n++) printf(“%d^3 is %d\n“, n, pow3(n)); }

  8. A function with two parameters called as values and with a returning value: Headers of functions (3/13) double func_name(double A, double B) { } The function for n-power of rational number floatpow_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; }

  9. 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

  10. A function with a parameter as a string Headers of functions (5/13) ??? func_name(char* A) { } The function returning number of ciphers in the string intnuminstr(char *s) { int n, count=0; for(n=0; s[n]!='\0'; n++) if(s[n]>='0'&&s[n]<='9') count++; return count ; }

  11. Headers of functions (6/13) int main(void) { chartxt1[] = "ab9bj65D9"; chartxt2[] = "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

  12. A function with parameters called as reference Headers of functions (7/13) ??? func_name(int *A, int *B) { } • Parameters are pointers The function for conversion from polar to Cartesian coordinates voidpolar2cart(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 }

  13. Headers of functions (8/13) int main(void) { float x=2.0; float y=90.0; printf("Magnitude is %fand phase is %f deg.", x, y); polar2cart(&x, &y); printf("Real part is %fand imag. part is %f", x, y); getchar(); return 0; } Source code: Ex53.c

  14. A function with parameter, which references the pointer to the first element of array (alike for strings) Headers of functions (9/13) The function for mean value calculation from vector of rational numbers floatmean(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 }

  15. 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

  16. Own type of variable can be defined by usingtypedef Headers of functions (11/13) typedef int t_mat[3][3] ; void func_name(t_mat A, t_matB) { } int func_name(t_mat A) { } t_mat func_name(t_mat A) { } !!! A function can return a value or pointer only (no array) !!!

  17. The function for determinant calculation from matrix 3 by 3 Headers of functions (12/13) typedef int t_mat[3][3]; intdet_mat(t_matA)// determinant of 3x3 matrix { intdet=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; }

  18. 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; } Headers of functions (13/13) Source code: Ex55.c

  19. A function can call the same function in its body Recursion of function (1/1) int func_name(intA) {… x = func_name(y); …} The function for factorial computation unsigned intfactorial(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; } Source code: Ex56.c

  20. Libraries of functions (1/10) • A library can be build-up using own set of functions: • my_lib.h:a file containing headers of our functions from the same-name file my_lib.c:a file containing source codes of our functions • #include”my_lib.h”:have to beinserted in our program, in whichfunctions form the library file my_lib.care called

  21. Libraries of functions (2/10) • In Code::Blocks: File > New > File my_lib.c +my_lib.hinto the directory of the project or specific own directory for own libraries

  22. Libraries of functions (3/10) • Setting of paths for compiler in Code::Blocks: • Settings > Compiler add paths with sources and headers

  23. Own library of functions for operations with 3 by 3 matrixes Libraries of functions (4/10) typedefint t_mat[3][3]; int det_mat(t_mat A);// determinant of A void print_mat(t_mat A);// printing A void gen_mat(t_mat A, int start, int stop);// gener. A void copy_mat(t_mat A, t_mat B);// copying A to B void add_mat(t_mat A, t_mat B);// A=A+B void sub_mat(t_mat A, t_mat B);// A=A-B void clr_mat(t_mat A);// zeroizing A header filematops.h • own types of variables definitions • header functions with definitions of types for all input and output parameters

  24. Libraries of functions (5/10) • it includes source codes for all functions according to header filematops.h #include<stdio.h> #include<time.h> #include<stdlib.h> typedefint 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++) { source codes of librarymatops.c

  25. 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 (6/10)

  26. 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 (7/10)

  27. 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 (8/10)

  28. 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 (9/10)

  29. Example of a program, which uses ownlibrarymatops.h 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); … Source code: Ex57.c + matops.c(h)

  30. Example (1/2) Create a library with functions for computing areas of 2-D geometric objects (build-up functions for rectangle, ellipse and triangle). • Header file for libraryareas2D.h doubles_rect(doublea, doubleb); double s_ell (doublea, doubleb); doubles_tri (doublea, doubleb);

  31. Library functions inareas2D.cpp Example (2/2) #include "areas2D.h" doubles_rect(doublea, doubleb) { return a*b;} double s_ell (doublea, doubleb) { return 3.1415*a*b;} doubles_tri (doublea, doubleb) { return 0.5*a*b;} Source code: Ex58.c + areas2D.c(h)

  32. TOPIC OF THE NEXT LECTURE Advanced data types THANK YOUFOR YOUR ATTENTION

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