Procedural Programming

Transcription

1 Exercise 3 (SS 2017) What will I learn in the 3. Exercise Functions Arrays Exercise(s) 1

2 Home exercise 2 (3 points) Write a program which allows the calculation of the mean of given integer values. The user is asked to input the numbers one after the other. When the user inputs a zero, the program prints the mean of the values entered and terminates. Why functions? Allow us to modularize a program and leads to the facts that a source code is: better readable better understandable easier to maintain easier to extend shorter than without functions Linux kernel has more than 15 milliones line of code (with functions) 2

3 Form of function type name([declaration list]) //functions body type : type of function, defines the return value (i.e.: int, void, etc.) name: name of the function (use a name which makes sense) declaration list: list of arguments, (each argument must have a data type) Function: return value and void A function must return a value according to its declaration. Example: int sum(int a, int b) int result; result = a + b; return result; The return statement exits the function If a function should not return a value, declare this function as a void function. 3

4 Functions: arguments properties Arguments are the input values of a function They have to be declared by data type and name (comma separated if more than one) They can be handled like local variables The arguments value is always a copy of that value which is used when the function is called Functions: arguments example int summinus2(int a, int b) return(--a + --b); int main() int a=5,b=5,sum; sum=summinus2(a,b); printf( a=%d, b=%d, sum=%d, a,b,sum); return 0; => Output : a=5, b=5, sum=8 4

5 Function: variables Local variables: variables which are declared within a function are only valid in that function => local scope Global variables: variables which are declared outside of any function are valid everywhere => global scope Hint: Take care if you use global variables Functions: recursion A function can call other functions A function can call itself => recursion If you want to use a recursion, take care that you avoid an endless recursion! Example: int findhighestdivisor(int a, int n) if (!(a%n)) return (a/n); return (findhighestdivisor(a, ++n)); 5

6 Functions: declaration and definition Before you can use (call) a function in C, the function must be known => Declare the function before using it The definition of the function can be done later (after the main function) Example Exercise 4 A program should calculate the sum from 1 up to n, what means: n sum = i i=0 Solve the problem twice - with a for loop which is embedded in a function and without a loop construct. Questions/Tasks - write a pseudo code for the with loop variant - draw a float chart for the variant without loop - write the program 6

7 Arrays in general An array is a data structure which consists of an orderered collection of elements Each element can be identified by an index Arrays can have more than one dimension One dimensional array(n) is like a vector with n elements or an table with one colum an n rows 2 dimensional array(n*m) is like a table with n columns and m rows.. Arrays: memory organization (1 dimensional array) An array always occupies an contiguos area of memory! int a[6];//array with 6 integers a[0]=11; a[1]=12; a[2]=13; a[3]=14; a[4]=15; a[5]=16; a[0] a[1] a[2] a[3] a[4] a[5] Memory

8 Arrays: memory organization (2 dimensional array) Even when you have a 2 or more dimensional array it is organized as a contiguos area of memory int matrix[2][3]; matrix[0][0]=0; matrix[0][1]=1; matrix[0][2]=2; matrix[1][0]=10; matrix[1][1]=11; matrix[1][2]=12; matrix[0][0] matrix[0][1] matrix[0][2] matrix[1][0] matrix[1][1] matrix[1][2] Memory Arrays: index Access to the different array elements is done by the index (integer) An index starts in C always with 0 => For an array with n elements the last index is always: n-1 Take care that you never use an index which is out of range Hint: C does not take care of that 8

9 Arrays: initializiation and default values An array can bei initialized when it is defined int a[6]=10,11,12,13,14,15; //is equal to int a[] =10,11,12,13,14,15; int matrix[2][3] = 0, 1, 2,10,11,12 ; //is equal to int matrix[][3] = 0, 1, 2,10,11,12 ; second area (here 3) must be defined Arrays: default values If I don t initialize my array, do the elements of my array have a default value? Answer: The values of global defined arrays are set to 0. The values of local defined arrays (i.e. in a function) are not set (random value). 9

10 Arrays: size of and number of elements How can I determine the space of memory which is used by an array respectively how can determine the number of elements in an array? Solution is: sizeof() sizeof(int); //returns the size of int int a[6]; sizeof(a); //returns 6*sizeof(int) sizeof(a)/sizeof(int) //returns 6 Exercise 5 A program should read in 5 integer values in an array and calculates (and prints out) the maximum and the minimum of the entered values. Questions/Tasks Find out algorithms for min and max and use functions for the implementation. The functions should also work for larger arrays. Draw the flowchart Write the program 10

11 Home exercise 3 Write a program which compare the length of two vectors of the form V1=(X1,X2,X3), V2=(Y1,Y2,Y3). The program should print out the result in the form: V1 > V2 or V1 < V2 or V1 = V2 The vectors should be read in into 2 arrays. The comparison of the vectors length should be realized by the function: int compveclen(int v1[], int v2[]) Hint: The length of a vector is calculated by V = x 2 + y 2 +z 2 Programming style Use spaces in source code (easier to read) Use BlockCodes Descriptive names for variables and use CamelCase. Example: (int nrofadders) Initialize your variables Use constant or defines for fixed values Use comments Avoid long lines and complex statements 11

12 //Exercise 4 #include <stdio.h> #include <stdlib.h> unsigned long long sumfromoneton(unsigned long long n) int main() unsigned int long long n double result; printf("calc sum from 1-n\n"); printf("enter n please:"); scanf("%llu",&n); result = (double)n/2 *(n+1); printf("\ngauss Result=%0.f\n",result); printf("\nloop Result=%llu\n",sumFromOneToN(n)); return EXIT_SUCCESS; //defined in stdlib unsigned long long sumfromoneton(unsigned long long n) unsigned long long sum; for(sum=0; n>0; n--) sum +=n; return sum; 3

13 //Exercise 5 Flowchart for function min/max mini(inarr[], n) min = inarr[--n],--n n >= 0 no return min yes min>inarr[n] no yes min = inarr[n] --n Flowchart for max Replace min with max, and change min>inarr[n] into max < inarr[n] 4

14 //Exercise 5 Flowchart for main program Start minmax i = 0 Input inarr [i] i ++ i < 5 yes no min = mini(inarr,n) max = maxi(inarr,n) Output min, max end minmax 5

15 #include <stdio.h> //Exercise 5 #include <stdlib.h> #define A_MAX 5 int mini(int inarr[], int n) int min; for (min=inarr[--n],--n; n >=0; --n ) if (min > inarr[n]) min = inarr[n]; return min; int maxi(int inarr[], int n) int max; for (max=inarr[--n],--n; n >=0; --n ) if (max < inarr[n]) max = inarr[n]; return max; int main() int intarr[a_max], i=0, min, max; do printf("please, input a number:"); scanf("%d",&intarr[i++]); fflush(stdin); while(i < A_MAX); min = mini(intarr,a_max); max = maxi(intarr,a_max); printf("\nmin:%d",a_max, min); printf("\nmax:%d",a_max, max); return EXIT_SUCCESS; 6