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Lecture 10: Reviews

Lecture 10: Reviews. Control Structures. All C programs written in term of 3 control structures Sequence structures Programs executed sequentially by default Selection structures Used to choose among alternative courses of action Three types: if , if … else , and switch

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Lecture 10: Reviews

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  1. Lecture 10: Reviews

  2. Control Structures • All C programs written in term of 3 control structures • Sequence structures • Programs executed sequentially by default • Selection structures • Used to choose among alternative courses of action • Three types: if, if … else, and switch • Repetition structures • Used to repeat an action when some condition remains true. • Three types: while, do … while and for

  3. Sequence Structures Normally, statements are executed one after the other in the order written

  4. Selection Structures - if • if statement if (condition) { statement(s); } • Only performs an action if the condition is true. • Example: • Flowchart if ( grade >= 60 ) { printf( “Passed\n” ); } if ( grade >= 60 ) { printf( “Passed\n” ); printf( “Congratulations!\n” ); } if ( grade >= 60 ) printf( “Passed\n” ); printf( “Congratulations!\n” );

  5. Selection Structures - if…else • If…else statement if (condition) { statement(s); } else { statement(s); } • Specifies an action to be performed both when the condition is true and when it is false. • Flowchart

  6. Selection Structures - if…else • Nested if…else statements • Test for multiple cases by placing if…else selection statements inside if…else selection statement • Once condition is met, rest of statements skipped if ( score >= 90 ) { printf( "The grade is 'A'.\n" ); } else if ( score >= 80 ) { printf( "The grade is 'B'.\n" ); } else if ( score >= 70 ) { printf( "The grade is 'C'.\n" ); } else if ( score >= 60 ) { printf( "The grade is 'D'.\n" ); } else { printf( "The grade is 'F'.\n" ); } >= 90: A 80 ~ 89: B 70 ~ 79: C 60 ~ 69: D < 60: F

  7. Selection Structures - if…else • if…else statements in sequence if ( score >= 90 ) { printf( "The grade is 'A'.\n" ); } else if ( score >= 80 ) { printf( "The grade is 'B'.\n" ); } if ( score >= 70 ) { printf( "The grade is 'C'.\n" ); } else if ( score >= 60 ) { printf( "The grade is 'D'.\n" ); } else { printf( "The grade is 'F'.\n" ); }

  8. default case occurs if none of the cases are matched Selection Structures - switch • switch statement • Useful when a variable or expression is tested for all the values it can assume and different actions are taken. • Format Series of case labels and an optional default case switch ( controlling expression ) { case value1: actions case value2: actions default: actions } • The switch statement can be used only for testing a constant integral expression. switch (grade) { case >= 90: … case >= 80: … ….. }

  9. Selection Structures - switch • switch statement with break statements switch ( controlling expression ) { case value1: actions; break; case value2: actions; break; default: actions; break; } • It causes program control to continue with the first statement after the switch statement.

  10. Selection Structures - switch • switch statement with break statements • Example switch ( n ) { case 1: printf( “The number is 1\n”); break; case 2: printf( “The number is 2\n”); break; case 3: printf( “The number is 3\n”); break; default: printf( “The number is not 1, 2, or 3\n”); break; }

  11. Selection Structures - switch • switch statement with break statements • Example switch ( n ) { case 1: printf( “The number is 1\n”); case 2: printf( “The number is 2\n”); break; case 3: printf( “The number is 3\n”); break; default: printf( “The number is not 1, 2, or 3\n”); break; }

  12. Repetition Structures • Two types of repetition structures • Counter-controlled repetition • Definite repetition: know how many times loop will execute • Control variable used to count repetitions • Sentinel-controlled repetition • Indefinite repetition • Used when number of repetitions not known • Sentinel value indicates "end of data entry” • Loop ends when user inputs the sentinel value

  13. Repetition Structures • Common error: Infinite loops are caused when the loop-continuation condition in a while, for or do...while statement never becomes false. To prevent: a) Make sure there is not a semicolon immediately after the header of a while statement. b) In a counter-controlled loop, make sure the control variable is incremented (or decremented) in the loop. c) In a sentinel-controlled loop, make sure the sentinel value is eventually input. j = 1; while (j <= 10) { printf(“%d\n”, --j); j++; } j = 1; while (j <= 10) { printf(“%d\n”, j); j--; } j = 1; while (j <= 10); { printf(“%d\n”, j); j++; } j = 1; while (j <= 10) { printf(“%d\n”, j); }

  14. while body condition Repetition Structures - while • while loop repeated until condition becomes false • Counter-controlled repetition • Sentinel-controlled repetition • Format while ( condition ) { statement(s); } • Flowchart

  15. Repetition Structures - while Counter-controlled while loop Loop repeated until counter reaches a certain value Count the number of iterations j = 1; while (j <= 10) { printf(“Good Luck\n”); j++; } j = 0; while (j < 10) { printf(“Good Luck\n”); j++; } j = 0; while (j <= 10) { printf(“Good Luck\n”); j++; } j = 1; while (j <= 10) { printf(“Good Luck\n”); j += 2; } j = -1; while (j <= 10) { printf(“Good Luck\n”); j += 3; }

  16. Repetition Structures - while • Sentinel-controlled while loop Loop repeated until user inputs the sentinel value • Sentinel value chosen so it cannot be confused with a regular input • Examples • Simple calculator • ATM menu interface • Prime number

  17. Repetition Structures - do…while • Similar to the while statement • Condition for repetition only tested after the body of the loop is performed. • All actions are performed at least once. • Format do { statement(s); } while ( condition ); • Flowcharting the do…while repetition statement

  18. Repetition Structures - do…while Examples counter = 1; while (counter <= 10) { printf( “%d\n”, counter); counter ++; } counter = 1; do { printf( “%d\n”, counter); counter ++; } while (counter <= 10); counter = 12; while (counter <= 10) { printf( “%d\n”, counter); counter ++; } counter = 12; do { printf( “%d\n”, counter); counter ++; } while (counter <= 10);

  19. Repetition Structures - for • Can loop a known number of times • Format when using for loops for ( initialization; loopContinuationTest; increment ) { statement(s); } initialization; while ( loopContinuationTest ) { statement(s); increment; } for (j = 1; j <= 10; j++) { printf(“%d\n”, j); } for (j = 10; j > 0; j -= 2) { printf(“%d\n”, j); } for (j = 10; j > 0; j--) { printf(“%d\n”, j); } Increasing/decreasing other than 1 increment decrement

  20. Nested Control Loops j • Nested while loops i = 1; while (i < 5) { j = 1; while (j < 5) { printf(“%d * %d = %d\n”, i, j, i*j); j++; } i++; } • Nested for loops for (i = 1; i < 5; i++) { for (j = 1; j < 5; j++) { printf(“%d * %d = %d\n”, i, j, i*j); } } i

  21. Nested Control Loops j • Nested while loops i = 1; while (i < 5) { j = 1; while ( j <= i ) { printf(“%d * %d = %d\n”, i, j, i*j); j++; } i++; } • Nested for loops for (i = 1; i < 5; i++) { for (j = 1; j <= i; j++) { printf(“%d * %d = %d\n”, i, j, i*j); } } i j <= i j <= i

  22. Nested Control Loops j • Nested while loops i = 1; while (i < 5) { j = 1; while ( j < 5 ) { printf(“%d * %d = %d\n”, i, j, i*j); j++; } i += 2; } • Nested for loops for (i = 1; i < 5; i += 2) { for (j = 1; j < 5; j++) { printf(“%d * %d = %d\n”, i, j, i*j); } } i

  23. Operators Arithmetic operators +, -, *, /, % Assignment operator = Arithmetic assignment operators +=, -=, *=, /=, %= Increment / decrement operators ++, -- Relational operators <, <=, >, >= Equality operators ==, != Logical operators &&, ||, !

  24. == and = Swapping both operators does not ordinarily cause syntax errors. int payCode = 0; payCode = 4; if (payCode == 4) printf(“You get a bonus!\n”); int payCode = 0; payCode == 4; if (payCode == 4) printf(“You get a bonus!\n”); int payCode = 0; payCode = 3; if (payCode == 4) printf(“You get a bonus!\n”); int payCode = 0; payCode = 3; if (payCode = 4) printf(“You get a bonus!\n”);

  25. Pre-increment and Post-increment • Pre-increment/Pre-decrement • Operator is used before the variable (++c or --c) • Variable is changed before the expression it is in is evaluated • Post-increment/Post-decrement • Operator is used after the variable (c++ or c--) • Expression executes before the variable is changed. c = 5; printf(“%d\n”, c++); printf(“%d\n”, c); c = 5; printf(“%d\n”, ++c); printf(“%d\n”, c); c = 5; c++; printf(“%d\n”, c); c = 5; ++c; printf(“%d\n”, c);

  26. Logical Operators x Logical AND - && Logical OR - || Logical NOT - ! y x y

  27. Logical Operators • Examples int F = 0, T = 1; int x, y; x = !240; x = !0; x = (F && 1) || (T || F); y = (T || !F) && (!F && T); x = !(T && F || 1) if (grade >= 80 && grade <90) printf(“B\n”); while ((x > 0) || (y > 10)) { x--; y--; }

  28. scanf and printf • scanf() • Used to obtain a value (values) from the user using standard input (usually keyboard). • Examples int num, j; float x; scanf( “%d”, &num); scanf( “%d%d”, &num, &j); scanf( “%f”, &x); scanf( “%d%d%f”, &num, &j, &x); scanf( “%d”, num); scanf( “%d%d”, num);

  29. scanf and printf • printf() int num = 3, j = 2; float x = 3.0; printf( “Good Luck!\n”); /* prints a string */ printf( “num = %d\n”, num); /* prints the value of a variable */ printf( “%d + %d = %d\n”, num, j, num+j); /* prints the value of an expression */ printf( “%c\n”, ‘b’); /* prints the character ‘b’ */ j = ‘a’; printf( “%c\n”, j); /* prints the character ‘a’ */ printf( “x = %f\n”, x); /* prints a floating-point number */ printf( “x = %.2f\n”, x ); /* prints result with 2 digits after decimal point */

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