Either-or decisions are easy. They’re similar to the 1 or 0 of low-level programming: True\/False, On\/Off, Yes\/No. When a third element appears, decision-making becomes more complex. To put it another way: That third element can drive both the programmer and the program crazy.
\n
\nFor example, consider a situation where a chunk of code must be executed when this condition is met:<\/p>\n
The value of x is equal to 38
\nor
\nThe value of y is in the range of 10 to 15<\/p>\n
Translating that requirement directly into a if<\/em> statement looks something like this:<\/p>\n That statement reads, left-to-right, like the condition stated above. As a seasoned programmer, however, I don't blindly trust multiple conditions within an if<\/em> statement. Normally I'd hurriedly wrap parentheses around part of the equation, but I'll let this one go for demonstration purposes. Here's sample code:<\/p>\n Below is a sample run using the values 38 for And here's a sample run using the values 5 and 9, which shouldn't meet the condition:<\/p>\n Other sample runs demonstrated that the code works, which is good, but it's not an excuse to be sloppy or assume anything.<\/p>\n If you have compiler warnings on, you'll see a message appear whenever you attempt to use more than one logical operator within an if<\/em> comparison:<\/p>\n The parentheses solution is this:<\/p>\n In this case, however, the parentheses aren't really needed thanks to the order of precedence: The My advice is to use parentheses whenever you're in doubt, which could imply all the time. Don't worry about any scourge attached to the parenthetical solution; if it works, and especially if it's more readable, consider it good.<\/p>\n","protected":false},"excerpt":{"rendered":" The either-or choices are easy to make. Add in a third item and — oh no! — you’re going to have to use your brain and some logic. Continue reading if( x==38 || y>=10 && y<=15 )<\/code><\/pre>\n\r\n#include <stdio.h>\r\n\r\nint main()\r\n{\r\n int x,y;\r\n\r\n printf(\"Enter a value for x: \");\r\n scanf(\"%d\",&x);\r\n printf(\"Enter a value for y: \");\r\n scanf(\"%d\",&y);\r\n\r\n if( x==38 || y>=10 && y<=15 )\r\n puts(\"The condition is acceptable\");\r\n\r\n return(0);\r\n}<\/pre>\nx<\/code> and 12 for y<\/code>, which should meet both conditions, with x<\/code> at 38 and the value of y<\/code> between 10 and 15.<\/p>\nEnter a value for x: 38\r\nEnter a value for y: 12\r\nThe condition is acceptable<\/code><\/pre>\nEnter a value for x: 5\r\nEnter a value for y: 9<\/code><\/pre>\nLine 12: warning: suggest parentheses around && within ||<\/code><\/p>\nif( x==38 || (y>=10 && y<=15) )<\/code><\/pre>\n&&<\/code> operator ranks higher than the ||<\/code> operator, and associativity goes left-to-right. Therefore the parentheses are unnecessary. They do, however, make the code more readable.<\/p>\n