# Lec9 - Lecture 9 Getting Loopy PIC 10A Todd Wittman Sec...

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1 Lecture 9: Getting Loopy PIC 10A Todd Wittman Sec 3.10 : Input Validation square6 So far we’ve assumed the user gives us proper input. But what if they don’t? Enter a number: four square6 When you do a cin statement, it actually returns a boolean: true if you were able to read the value correctly, false if it failed to read the specified type. square6 Returns the boolean true for a success, so we can use cin in an if statement. square6 Alternatively you could use the member function cin.fail( ) described in Sec 4.4.

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2 Example: Input Validation int main ( ) { int x; cout << “Enter a number: “; if ( cin >> x ) { cout << “Your number is “ << x << “.\n”; return 0; } else { cout << “Supposed to be a number.”; return 1; } } This will end the program. Use the return command with caution. This line does 2 things: 1.) Gets input x from user. 2.) Checks if read successful. Sec 3.6 : The while loop square6 Sometimes it’s useful to repeat a block of code, like HW 3. square6 We call a block of code that is repeated a loop . square6 Each repetition of the code is called an iteration . square6 The while loop acts like a repeating if statement, repeating the code below it as long as the boolean statement is true. Also called a stopping condition . while ( statement is true ) { ** STATEMENTS ** } square6 The braces { } enclose the code to repeat. square6 Like with if , indenting makes it easier to read.
3 Example of a while loop int x = -1; while ( x <= 0 ) { cout << “Enter a postive number: “; cin >> x; } cout << “Your number is “ << x << “.\n”;

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