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Computers and Programming CPC

Computers and Programming CPC. The 2 nd lecture Jiří Šebesta. TOPIC. Expressions Arithmetic conversions Operators Statements in C – introduction Selection statements Iteration statements I. Expressions (1/3). Operand: variable, constant or function calling returning a value.

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Computers and Programming CPC

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

  2. TOPIC Expressions Arithmetic conversions Operators Statements in C – introduction Selection statements Iteration statements I.

  3. Expressions (1/3) • Operand: • variable, constant or function calling returning a value Expression: serves to computing value consists of operands and operators • Operator: • symbol defining anarithmetic, 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; } Operandsas 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, shortconverted toint • …floatconverted todouble • If one operand is of the type … • …double, the second converted todouble • …long, the second converted tolong • …unsigned, the 2nd converted tounsigned

  7. Arithmetic conversions (2/2) 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 Example: arithmetic conversion Example: Ex09.c

  8. int a=1, b=6; a = -a; //changing sign b = !b; //negation printf("%3d\n", a);//-1 printf("%3d\n", b);//0 Operators (1/10) • Unary (a single operand): • changing a sign; • logic negation; • etc. • Binary (two operands): • arithmetic (addition, division, …); • logic (and, or, xor, …); • comparison (>, , ==, , <, , …); • assignment (=, …). 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

  9. Operators (2/10) Arithmetic

  10. Example: priority ofarithmetic operators (highernumberin col. of priority = lower priority) Operators (3/10) int a=3, b=12, c=7; intx, 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); Example: Ex12.c

  11. Comparison Operators (4/10) inta =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 Example: Ex13.c

  12. results of comparison operator • 0 = false • or • 1 = true • comparison operators can be used in complex expressions for testing of complicated conditions Operators (5/10) 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 <= b + c != a;//(3 <= (12 + 7)) != 3 =//(3 <= 19) != 3 => z = 1; Example: Ex14.c

  13. Logic Operators (6/10) 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 Example: Ex15.c

  14. Bit-wise Operators (7/10) 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 Example: Ex16.c

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

  16. Increment / decrement Operators (9/10) 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); Increment, decrement:priority = 2 Example: Ex17.c

  17. Assignment Operators (10/10) 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 <<= 2;//00000100b=> 00010000b s2 >>= 2;//00000100b=> 00000001b printf( "%3d\n", s1); printf( "%3d\n", s2); Example: Ex18.c

  18. Statements – introduction (1/4) • If a statement does not cause • control transfer to another part of the program • program interruption • then statements are executed sequentially Program:a sequence of statements (incl. expression statements, e.g. function calling) • 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. Empty statement Statements – introduction (2/4) if(err) goto end; // in case of error go to end c++; // otherwise increment end: ; // label and empty command an empty block {} hasthe same meaning as a empty statement • Expression statement: • assignments • function calling • etc.

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

  21. Compound statements – an example Statements – introduction (4/4) 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; }

  22. Selection statements (1/7) if(test) statement; if(test) statement_this; else statement_that; condition - true - false Conditioned statement: char day = '1'; if(day<48 || 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");

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

  27. Selection statements (6/7) 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; } Switch statement:when choosing from more than two possibilities • leaving • the switch body expression in case of another value

  28. Selection statements (7/7) printf("Which girl should go to the cinema with me?\n") srand(time(NULL)); switch(rand()%9)// random number from 0 to 8 { case0: printf("Jana");break;//if rand()%9 is 0 case1: printf("Eva");break;//if rand()%9 is 1 case2: printf("Klara");break;//if rand()%9 is 2 case3: printf("Milena");break;//if rand()%9 is 3 case4: printf("Dominika");break;//if rand()%9 is 4 case5: printf("Erika");break;//if rand()%9 is 5 case6: printf("Petra");break;//if rand()%9 is 6 case7: printf("Zuzana");break;//if rand()%9 is 7 default: printf("alone");//if rand()%9 is not from 0 to 7, i.e. 8 } Switch statement – an example Example: Ex20.c

  29. for Iteration statements I. (1/5) 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); None parameter is compulsory:for( ; ; ) is an infinite loop Example: Ex21.c

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

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

  32. Example - numeric integration of sin(x) for interval from 0 to π Iteration statements I. (4/5) •  Program: #include <stdio.h> #include <stdlib.h> #include <math.h> #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 Calculation:

  33. Iteration statements I. (5/5) 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); } Example: Ex22.c

  34. TOPIC OF THE NEXTLECTURE Statements II. Strings Libraries stdio.h and string.h THANK YOUFOR YOUR ATTENTION

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