1. Computers and Programming CPC The 2 nd lecture Jiří Šebesta

2. TOPIC 1.Expressions 2.Arithmetic conversions 3.Operators 4.Statements in C – introduction 5.Selection statements 6.Iteration statements I.

3. Expressions (1/3) Expression: – serves to computing value – consists of operands and operators Operand: – variable, constant or function calling returning a value Operator: – symbol defining an arithmetic, logic, assignment, comparison and other operation using operands

4. Expressions (2/3) int main(void) { int y1, y2, a=10, b=6; char c; y1 = a + b; // a, b are operands y2 = a / b; // +, / are operators printf("%3d\n", y1); printf("%3d\n", y2); scanf("%c", &c); return 0; } Operands as variables Example: Ex06.c + Ex07.c

5. Expressions (3/3)... #include "math.h" // library for math. functions int main(void) { double y, x = 10000.2501; char c; y = sqrt(x); printf("Square root of %10.4f is %10.8f\n", x, y); scanf( "%c", &c); return 0; } Operands as returning value from function calling Example: Ex08

6. Arithmetic conversions (1/2) All operands of the type … – … char, short converted to int – … float converted to double If one operand is of the type … – … double, the second converted to double – … long, the second converted to long – … unsigned, the 2 nd converted to unsigned

7. Arithmetic conversions (2/2) Example: arithmetic conversion Example: Ex09.c int a, b, c; float d, e; char f = 'A'; a = 3/5; // {int} = {int}/{int} b = 3/5.0; // {int} = {int}/{float} c = f+1;// {int} = {char->int}+{int} d = 3/5; // {float} = {int}/{int} e = 3/5.0; // {float} = {int}/{float} printf("%3d\n", a); // 0 printf("%3d\n", b);// 0 printf("%3d\n", c);// 66 (ASCII of 'A' is 65) printf("%6.2f\n", d); // 0.00 printf("%6.2f\n", e); // 0.60

8. Operators (1/10) int a=1, b=6; a = -a; //changing sign b = !b; //negation printf("%3d\n", a); //-1 printf("%3d\n", b); //0 int a=1, b=6, c, d, e; c = a<=b; d = a!=b; //not equal e = a==b; printf("%3d\n", c); //1 printf("%3d\n", d); //1 printf("%3d\n", e); //0 Example: Ex10.c + Ex11.c Unary (a single operand): – changing a sign; – logic negation; – etc. Binary (two operands): – arithmetic (addition, division, …); – logic (and, or, xor, …); – comparison (>, , ==, , <, , …); – assignment (=, …).

9. Operators (2/10) Arithmetic

10. Operators (3/10) Example: priority of arithmetic operators (higher number in col. of priority = lower priority) Example: Ex12.c int a = 3, b = 12, c = 7; int x, y, z; x = -a + b % c; //-3 + (12 % 7) = -3 + 5 = 2 y = -(a + b) % c; //-(3 + 12) % 7 = -15 % 7 = -1 z = (-a + b) % c; //(-3 + 12) % 7 = 9 % 7 = 2 printf("%3d\n", x); printf("%3d\n", y); printf("%3d\n", z);

11. Operators (4/10) Comparison Example: Ex13.c int a = 1, b = 6, c, d, e; c = a <= b;//a is smaller or equals b, c = 1 d = a != b;//a does not equal b, d = 1 e = a == b;//a equals b, e = 0

12. Operators (5/10) Example: Ex14.c results of comparison operator 0 = false or 1 = true comparison operators can be used in complex expressions for testing of complicated conditions int a = 3, b = 12, c = 7; x = a + b == c; //(3 + 12) == 7 => x = 0 y = a + (b == c); //3 + (12 == 7) = 3 + 0 => y = 3 z = a z = 1;

13. Operators (6/10) Logic Example: Ex15.c int a = 3, b = 12, c = 7; x = !a || b; //!3 || 12 => 0 || 1 => x = 1 y = !(a || b);//!(3 || 12) => !(0 || 1) => y = 0 z = a || b && c;//3 || (12 && 7) => 0 || (1 && 1) //=> z = 1

14. Operators (7/10) Bit-wise Example: Ex16.c int b = 12, c = 7; x = b >> 2; //1100b => 0011b = 3 y = b & c; //1100b & 0111b = 0100b = 4 z = b ^ c; //1100b ^ 0111b = 1011b = 11

15. Operators (8/10) Truth table for bit-wise operators

16. Operators (9/10) Increment, decrement: priority = 2 Increment / decrement Example: Ex17.c double r1, r2, a1=5.1, a2=5.1, b=4.2; r1 = a1++ + b; //r1 = 5.1 + 4.2 = 9.3 //a1 = a1 + 1 = 6.1 r2 = ++a2 + b; //a2 = a2 + 1 = 6.1 //r2 = 6.1 + 4.2 = 10.3 printf("%6.2f\n", a1); printf("%6.2f\n", r1); printf("%6.2f\n", a2); printf("%6.2f\n", r2);

17. Operators (10/10) Assignment Example: Ex18.c double r1=2.2, r2=3.3, a1=4.4, a2=5.5; int s1=4, s2=4; r1 += a2-a1; //r1 = r1 + (a2 - a1) r2 /= a2-a1; //r2 = r2 / (a2 - a1) printf("%6.2f\n", r1); printf("%6.2f\n", r2); s1 00010000b s2 >>= 2; //00000100b => 00000001b printf( "%3d\n", s1); printf( "%3d\n", s2);

18. Statements – introduction (1/4) Program:a sequence of statements (incl. expression statements, e.g. function calling) If a statement does not cause – control transfer to another part of the program – program interruption then statements are executed sequentially Standard statement (ANSII C/C++): given by the reserved word (e.g. for, if, else) notice: reserved words are blue in MS Visual Studio or Code:Blocks – they may not be used as names of variables

19. Statements – introduction (2/4) an empty block { } has the same meaning as a empty statement if(err) goto end; // in case of error go to end c++; // otherwise increment end: ; // label and empty command Empty statement Expression statement: – assignments – function calling – etc.

20. Statements – introduction (3/4) C ++ ; A = cos(b) + c; Expression statement – an example Compound statement: a sequence of statements closed in braces – {stat1; stat2; stat3;} Compound statement can contain another compound statement: – a nested block – a superior block

21. int main( void) { char text[40] = "The momentary laps of..."; int n, conv = 0; for(n=0; n<strlen(text); n++) { if( text[n]==' ') { text[n+1] = text[n+1] - 32; conv++; } printf("Mod.: %s (%d changed)",text, conv); getchar(); return 0; } Statements – introduction (4/4) Compound statements – an example

22. Selection statements (1/7) if(test) statement; if(test) statement_this; else statement_that; char day = '1'; if(day 57) printf("Not a number\n"); else if(day>48 && day<56) // 1,2,3,…7 printf("Now is the %cth day\n", day); else printf("An invalid day number\n"); Conditioned statement: condition - true - false

23. Selection statements (2/7) if

24. Selection statements (3/7) if - else

25. Selection statements (4/7) if – else if – else

26. Selection statements (5/7) Test ? Statement_this : Statement_that; int a, b, c; a = 3; b = 9; c = (a > b) ? a : b; // c = 9 // if (a>b) c = a; // else c = b; Ternary condition ?: (operator) condition statement for true condition Selection of higher value: statement for false condition Example: Ex19.c

27. Selection statements (6/7) Switch statement: when choosing from more than two possibilities expression with integer value switch(value) { case 1 : statement_1; break; case 2 : statement_2; break; case 3 : statement_3; break; case 4 : statement_4; break; default: statement_other; } leaving the switch body expression in case of another value

28. printf("Which girl should go to the cinema with me?\n") srand(time(NULL)); switch(rand()%9)// random number from 0 to 8 { case 0: printf("Jana"); break; //if rand()%9 is 0 case 1: printf("Eva"); break; //if rand()%9 is 1 case 2: printf("Klara"); break; //if rand()%9 is 2 case 3: printf("Milena"); break; //if rand()%9 is 3 case 4: printf("Dominika"); break; //if rand()%9 is 4 case 5: printf("Erika"); break; //if rand()%9 is 5 case 6: printf("Petra"); break; //if rand()%9 is 6 case 7: printf("Zuzana"); break; //if rand()%9 is 7 default: printf("alone"); //if rand()%9 is not from 0 to 7, i.e. 8 } Selection statements (7/7) Switch statement – an example Example: Ex20.c

29. Iteration statements I. (1/5) None parameter is compulsory: for( ; ; ) is an infinite loop for(init; test; update) statement; char text[] = "Vjku\"oguucig\"ku\"ugetgv#"; unsigned int n; for(n=0; text[n]!='\0'; n++) // loop for all chars in str if(text[n]!=' ') // excluding space text[n] -= 2; // character code shift printf("%s\n", text); for Example: Ex21.c

30. Iteration statements I. (2/5) for

31. Iteration statements I. (3/5) Trapezoid approximation: area for one section: Example - numeric integration Generally: Integral: is a sum of all partial areas for all sections

32. Iteration statements I. (4/5) Calculation: Example - numeric integration of sin(x) for interval from 0 to π Program: #include #define pi 3.141529 int main(void) { double a[101], f[101]; //a = angle, f = func. value int n, i; double sum = 0, step; //step = lenght of interval int start = 3, stop = 100; // max. is 100

33. Iteration statements I. (5/5) Example: Ex22.c for(n=start;n<=stop;n++) { sum = 0; for(i=0;i<=n;i++) { a[i] = 180.0*i/(n*1.0); f[i] = sin(a[i]*pi/180.0); } step = pi/(1.0*n); for(i=0;i<n;i++) sum += f[i]*step + (f[i+1]-f[i])*step/2.0; printf("\nFor %d intervals is integral %10.8f.", n, sum); }

34. TOPIC OF THE NEXT LECTURE 1.Statements II. 2.Strings 3.Libraries stdio.h and string.h THANK YOU FOR YOUR ATTENTION