1. Conditional Expressions

2. Control Statements
A control statement will or will not be executed based on the value
of the conditional expression
scanf("%d", &pressureValue);
while (pressureValue <= MAX_PRESSURE) {
if (pressureValue == NOMINAL_VALUE)
printf("Pressure is nominal\n");
else
printf("Pressure is %d pounds\n", pressureValue);
for (i = 5; i <= pressureValue; i = i + 10)
printf("+");
printf("\n");
} // End while

3. Boolean Type
A conditional expression evaluates to a value of true or false
These are the two values for the Boolean type named after the mathematician George Boole
When a conditional expression is evaluated, it results in a value of type Boolean
In the C programming language there is no explicit Boolean type. Instead, false is 0 and true is any non-zero value. Many C programs use a #define macro to set a Boolean variable to true or false
#define FALSE 0
#define TRUE 1
Conditional expressions are also called Boolean expressions
A conditional expression is used whenever a true or false decision needs to be made about the value of certain variables or constants in a program

4. Expression Contents
A conditional expression in C may contain any valid mathematical expression
It may also contain relational operators and logical operators
In addition, it may contain one or more function calls that return a value

5. Relational Operators ==,!= Equivalent, Not equivalent
<, <= Less than, Less than or equals
>, >= Greater than, Greater than or equals
if (A == B) C = 5;
if (A != B) C = 10;
for (i = 0; i < MAX_INDEX; i++) printf("*");
if (A <= B) D = 20;
while (A > B) B++;
if (A >= B) D = 40;
A = B <= C;
D = A == B;

6. Logical Operators && Logical AND || Logical OR ! Logical NOT
if ( (A == B) && (C <= D) ) E = 5;
if ( (A != B) || (C >= D) ) F = 10;
while ( !(A == B) ) B++;
if ( !((A >= B) && (C <= D) || (E != F)))
G = 100;
A = B || C;
D = A && B;

7. Boolean Algebra NOT false = true NOT true = false true AND true = true
true AND false = false
true OR true = true
true OR false = true
false AND false = false
false OR false = false
if (0 || 0) printf("Does false OR false = true?");
if (0 && 0) printf("Does false AND false = true?");

8. More Examples ch1 = 'a'; ch2 = 'a';
printf("ch1 OR ch2 = %d\n", ch1 || ch2); // 1
printf("ch1 AND ch2 = %d\n", ch1 && ch2); // 1
ch1 = 'd';
ch2 = 'f';
ch2 = '\0';
printf("ch1 AND ch2 = %d\n", ch1 && ch2); // 0

9. Example with Logical and Relational Operators
while ( (w <= x) && ( y >= z) ) {
if ( (w < MAX_HEIGHT) || (y > MAX_DISTANCE) )
w = w + newHeight;
y = y - newDistance;
newValuesUsed = TRUE; }
else
w = w + oldHeight;
y = y - oldDistance;
newValuesUsed = FALSE;
} // End if
if ( !silentMode ) // Use of negative logic
printf("Height: %d Distance: &d\n", w, y);
} // End while

10. Operator Precedence Rule of thumb: Avoid complicated
Precedence refers to the order in which operations are evaluated in an expression a = w * x + !y || -u – v && b % c / d++;
There is a hierarchy of rules that tells which operators are evaluated before other operators (i.e., unary before binary operators, multiplication before addition, relational operators before logical operators)
The highest precedence goes to parentheses
Rule of thumb: Avoid complicated
expressions and use parentheses

11. Special Notes Avoid complicated conditional expressions, especially
When they are not a part of the original procedural design
When they are created just to get the program to finally run
Use meaningful names for Boolean variables and declare them of type int
Ex. valueFound, errorStatus, moreData
Do not compare Boolean variables to TRUE or FALSE
if (valueFound == TRUE) X = 5; // Bad practice
if (valueFound) X = 5; // Good practice
if (valueFound == FALSE) X = 5; // Bad practice
if (!valueFound) X = 5; // Good practice

12. Special Notes (continued)
Beware of the bitwise operators; they are not the same as the logical operators
& bitwise AND
| bitwise OR
if (4 & 2) printf("Is this true?"); // Bitwise
if (4 && 2) printf("Or is this true?"); // Logical
Do not user == or != operator with values of type float
double v = ;
. . .
if (v == ZERO) X = 10; // Bad
if ((v >= ) && (v <= 0.001)) x = 10; // Good 