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Lec-5-IF-ELSE-SWITCH Programming Fundamentals.pptx
- 1. PROGRAMMING FUNDAMENTALS Lecturer: Syed MWaqas Shah NUML Multan LECTURE 5 National University of Modern Languages (NUML)
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- 3. Program types • Allprograms can be written in terms of only three control structures, namely, – the sequence structure, – the selection structure (Branching) and – the repetition structure (Looping).
- 4. Selection/Conditional statements • Selectionstatements cause one section of code to be executed or not depending on a conditional clause. – if statement – switch statement
- 5. The if statement •Used where the execution of an action depends on the satisfaction of a condition. – if condition is true -> action is done T
- 6. The if statement •Used where the execution of an action depends on the satisfaction of a condition. – if condition is true -> action is done – if condition is false -> action is not done F
- 7. The if statement Syntax if(condition) { statement1; statement 2; …. statement n; } Condition to be checked Any statement that results in True or False T F
- 8. The if statement •Develop a system that tells the user that he is over-speeding if his speed crosses120km/hr.
- 9. The if statement •Develop a system that tells the user that he is over-speeding if his speed crosses120km/hr. • Pseudocode IF speed is greater than 120km/hr THEN print “over-speeding”
- 10. The if statement if(speed>120) {cout<<"over speeding"<<endl; cout << "reduce speed now"; } … … … T F T F
- 11. The if statement(Example)
- 12. If - else •if is a single-selection statement which performs an indicated action only when the condition is TRUE; otherwise the action is skipped. • if-else is a double-selection statement which performs an action when the condition is TRUE and a different action when the condition is FALSE.
- 13. If - else •Used where there are different actions to be executed depending on the result of a given condition. – if condition is true -> action is done – if condition is false -> a different action is done
- 14. If - else •Syntax: if (condition) {statement1; statement 2;…. statement n; } else {statement1; statement 2;….statement n; } • Note: if the specified condition is true, then all the statements in the first curly braces will be executed, else all the statements in the next curly braces will be executed.
- 15. If - else •Determine whether a number is positive or negative. • Pseudocode • IF number is greater than or equal to 0, THEN print “positive” • ELSE print “negative”
- 16. If - else if(number>=0) cout<<"number is positive"; else cout<<"number is negative"; NOTE: {} are not used here
- 17. If – else(example)
- 18. If - else •TRY ME! : for positive numbers add half the number to y. For negative numbers, subtract half.
- 19. If – else(cont.)
- 20. Some notes • Ifthere is only one statement following the if, then the curly braces are optional • If there are multiple statements, the braces are necessary • Same is true for the statements following the else
- 21. Some notes – E.g. if(a<b) a=b+1; cout<<"print A"<<a; Output (if condition is true) ⮚ a = b+1; ⮚ the cout statement is ignored in this case because of the missing { }
- 22. Some notes • Anif can exist without an else. • An else, without an if has no meaning.
- 23. The else ifkeyword • Used where there are multiple actions to be executed based on different conditions. – if condition is true -> action is done – if condition is false -> next condition is checked
- 24. The else ifkeyword • Syntax: if (condition) {statement1; statement 2;…. statement n; } else if (condition 2) {statement1; statement 2;….statement n; } else {statement1; statement 2;….statement n; }
- 25. The else ifkeyword if (x==0) {cout << " x is ZERO" <<endl;} else if (x>0) {cout << " x is positive" <<endl;} else {cout << " x is negative" <<endl;}
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- 27. The else ifkeyword • Additional alternative control paths • Conditions evaluated in order until one is met; inner statement (or statements) are then executed • If multiple conditions are true, only first condition is executed, the remaining are ignored
- 28. The if ,else keyword with Multiple Conditions • Print A if the given number is positive And less than 10, else print B.
- 29. IF- else (multiplecondition)
- 30. Nested if statements •An if statement within the executable block of another if statement • Use? • Used where several conditions need to be met for the execution of an action. • Is this completely true? How?
- 31. Nested if statements •Conditions are checked in order, i.e. the inner condition is checked only if the outer condition is satisfied. – if condition is true -> inner condition is checked – if inner condition is true -> action is done
- 32. Nested if statements •Syntax: if (condition) {if (condition) statement1;//(…. to n) else statement; } else {statement1;statement 2;…. statement n; }
- 33. Nested if statements •Determine whether the number is positive even, positive odd, or zero. • Pseudocode IF number is greater than 0, IF number is divisible by 2, THEN print “positive even” ELSE print “positive odd” ELSE print “zero”
- 34. Nested if statements if(num>0) {if ((num%2)==0) cout << "positive even" << endl; else cout << "positive odd" << endl; } else cout << "zero" << endl;
- 35. Nested if statement(example)
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- 37. If else-if if (day== 1) cout<< "Sunday”; if (day == 1) cout<< "Sunday”; if (day == 2) cout << "Monday”; else if (day == 2) cout<< "Monday”; if (day == 3) cout << "Tuesday”; else if (day == 3) cout<< "Tuesday”; if (day == 4) cout << “Wednesday”; else if (day == 4) cout <<"Wednesday”; Here, each if condition will be checked even if the true one is found earlier on. Here, the compiler will skip the remaining if conditions following the true one.
- 38. switch-statement Syntax • switch(selector) // controlling statement { case label_1: statement_Sequence_1 break; case label_2: Statement_Sequence_2 break; case label_n: Statement_Sequence_n break; default: Default_Statement_Sequence } 33
- 39. The Controlling Statement •The value in switch statement is compared to the constant values after each "case" - When a match is found, the code for that case is used 34
- 40. The break Statement •The break statement ends the switch-statement - Omitting the break statement will cause the code for the next case to be executed! - Omitting a break statement allows the use of multiple case labels for a section of code • case 'A': case 'a': cout << "Excellent."; break; • Runs the same code for either 'A' or 'a' 35
- 41. The default Statement •If no case label has a constant that matches the controlling expression, the statements following the default label are executed - If there is no default label, nothing happens when the switch statement is executed - It is a good idea to include a default section 36
- 42. Switch (example) • Takeinput from the user. Print the following lines w.r.t to the input – If user input = 1 Print “It is case 1” 🡪 – If user input = 2 Print “It is case 2” 🡪 – If user input = 3 Print “It is case 3” 🡪 – Otherwise Print “default” 🡪
- 43. The switch statement cout<<"Enter a number "; cin >> a; switch(a) { case 1: cout <<"it is case 1n"; break; case 2: cout <<"it is case 2n"; break; case 3: cout <<"it is case 3n"; break; default: cout <<"it is default"; break; }
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- 45. Write a programthat takes an integer as input from user and do following things ∙ If the number is multiple of 5 then display "Number is a multiple of 5" ∙ If it is not multiple of 5, then check whether it is a multiple of 3 or 2 and display "The number is multiple of 3 but not 5" or "The number is multiple of 2 but not 5".
Editor's Notes
- #15 Evaluate condition if (x%2==0) If true, evaluate inner statement y += x/2; Otherwise, do nothing
- #16 Evaluate condition if (x%2==0) If true, evaluate inner statement y += x/2; Otherwise, do nothing
- #18 Evaluate condition if (x%2==0) If true, evaluate inner statement y += x/2; Otherwise, do nothing