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# Decision control

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### Decision control

1. 1. C Programming Language By: Yogendra Pal yogendra@learnbywatch.com Dedicated to My mother and Father
2. 2. t y Keep your notebook with you. Write important point and questions that comes in your mind Solve Mind band exercise. C Rewind when not clear Ask Questions by call or SMS or by mail Keep Watching Keep Learning THIS IS DECISION CONTROL 2
3. 3. Need • Consider a problem: – Write a program which take a number as a input and print it if it is an even number. – This problem can not solved by calculation or arithmetic expression. – We need to take decision here. 3
4. 4. Decision statements • To change the control flow of a program we use: – Branching statements : cause one section of code to be executed or not executed, depending on a conditional clause. – Looping statements : used to repeat a section of code a number of times or until some condition occurs. 4
5. 5. Branching Statements : 1 • if Statements – General form: if(condition) statement; • if Condition is true (non-zero), the statement will be executed. • if the condition is false (0), the statement will not be executed. 5
6. 6. An Example • Write a program which take a number as a input and print it if it is an even number. • == is a relational operator that represents “equal to”. – Eg. if (number % 2 == 0) printf(“It is an even number”); • This statement reads – “if the number%2 is equal to zero print ‘it is an even number’ ” 6
7. 7. Relational operator Operator Meaning <= Less than OR equal to < Less than >= Greater than or equal to == Equal != Not equal 7
8. 8. Logical Operator Operator Meaning || or && and 8
9. 9. Multiple Statements • Put all statements inside the curly { } braces. if(condition) { statement 1; statement 2; statement 3; } 9
10. 10. Problems • Input cost price and selling price of an item through the keyboard and write a program to determine the profit or loss. • Write a program to determine whether the year (input from keyboard) is a leap or not. • Write a program that take a character as a input and determine whether the character entered is a capital letter or small letter or a number. 10
11. 11. Branching Statement : 2 • else statement: • An alternate form of the if statement:- if(condition) If condition is true statement; execute this statement else otherwise statement; execute this statement • Write a program which take a number as a input and print it if it is an even number otherwise print “you entered ODD number”. 11
12. 12. Nested if - else if(condition) if(condition) if(condition) { statement; if(condition) else statement; statement; } if(condition) else { statement; if(condition) statement; else statement; } 12
13. 13. Nested if - else if(condition) if(condition){ statement; statement 1; else if (condition) statement 2; statement; } else if (condition) else if (condition){ statement; statement 1; else statement 2; statement; } else { statement 1; statement 2; } 13
14. 14. A problem • Write a program which take an operator (+, -, * or /) as an input and perform the operation according to the input. • Like: – a = 10; – b = 2; – Input = ‘+’ output = 12; – Input = ‘-’ output = 8; 14
15. 15. Branching Statement : 3 • switch statement – An alternative to the chain of if / else statements. switch (expression) • General form: { case constant_1: statement; break; Case case constant_2: label statement; default: statement; break; } 15
16. 16. Rules to use switch • Duplicate labels are not allowed. • Expression must evaluate an integer, character or enumeration. • Case labels can be in any order and must be constant. • Default label can be put anywhere in the switch. • No two case have the same value. 16
17. 17. If-else / switch • Break statement causes the program to go to the end of the switch. switch (operator) if(operator == „+‟){ { result += value; case „+‟: }else if (operator == „-‟){ result += value; resultbreak; -= value; case „-‟: }else { result -= value; printf(“Unknown operator %c n”,operator); break; } default: printf(“Unknown error %c n”, operator); } 17
18. 18. Conditional Operator • Works as if-else statement. • Condition ? Statement 1 : Statement 2; • If condition is true statement 1 will execute other wise statement 2. – ( a <= 5) ? 0 : 100; 18
19. 19. Operator Precedence Operator Operation Precendence () Parentheses Evaluate First, Innermost first, Left to right. -, +, --, ++, sizeof, (type) Unary operators Right to left *, / or % Multiplication, Division or Left to right. modulus + or - Addition and subtraction Left to right. <, <=, >, >= Relational operators Left to right. == != Equality operators Left to right. && Logical and Left to right. || Logical or Left to right. ?: Conditional operator Right to left = Assignment (Multiple) Right to left. 19
20. 20. Mind Bend • Write a program that accept a character from keyboard and convert as follows: – If it is uppercase then convert in lowercase letter. – If it is lowercase then convert in uppercase letter. – If it is other then alphabet print error message. • Write a program which take two sides of a rectangle and determine whether the given sides are of a rectangle or a square. 20
21. 21. To get complete benefit of this tutorial solve all the quiz on www.learnbywatch.com For any problem in this tutorial mail me at yogendra@learnbywatch.com with the subject “C” For Other information mail at info@learnbywatch.com Keep Watching Keep Learning NEXT IS LOOPS 21