Using Pre-written C Functions Need the following information –Name of the function –Types of the input parameters –Return type of the function Use the necessary include –#include for math functions –#include for rand function

Examples of Function Calls rand –ranNum = 1 + rand()%99; –ranYearNinties = rand()%10; math –difference = abs(price-cost); –phi = (1 + sqrt(5))/2; –distance = sqrt(pow(x,2)+pow(y,2));

Conditional Expressions Relational Operators –> (greater than) –< (less than) –>= (greater than or equal to) –<= (less than or equal to) –== (equal to – notice the TWO equal signs) –!= (not equal to)

Conditional Expressions Allow comparison of two primitive types Examples –b*b >= 4*a*c –money < 1000 –score != 21 Always evaluate to 1 or 0 –1 represents true –0 represents false

Complex Boolean Expressions Boolean Operators –&& (and) –|| (or) –! (not) Used to put together conditional expressions Examples –(age >= 21) && (age <= 65) –(b != 0) && (a/b > 0)

And, Or, Not and (&&) –Only true if both clauses are true –IT IS INCORRECT TO DO SOMETHING LIKE 21 <= age <= 65. The proper expression is (21 <= age) && (age <= 65). or (||) –True as long as at least one clause is true –Checks conditions in order, from left to right. not (!) –Negates value of the original expression

Standard If Statement if ( ) stmt1; else stmt2; stmtA; stmtB; Evaluate the boolean expression If it is true, execute stmt1 If it is not, execute stmt2 Then, in both cases, proceed to stmtA and continue.

Block of Statements if ( ) { stmt11; stmt12;. stmt1n; } else { stmt21; stmt22;. stmt2m; } stmtA; stmtB; Same as before But if the boolean expression is true, statements 11 through 1n all get executed in order Otherwise, if it is false, statements 21 through 2m all get executed in order In all cases, one or the other set of statements get executed, never both, and never neither. Afterwards, stmtA is always executed, regardless of the value of the boolean expression

Else-If Clause if ( ) else if ( ) else if ( ) else stmtA Now, we check boolean expressions in order When we find the FIRST true one, we execute the statement corresponding to it. If none are true, we execute the statement in the else clause Then, we continue to stmtA.

Notes about if statement All else if and else clauses are optional No “else if” or “else” is possible without a preceding and matching “if”. A block of statements can be used for any clause, but is not necessary. They can be mixed with clauses that don’t have a block. Be very careful about forming boolean expressions. Their order and form matter.

Nested If Statements Definition: an if statement inside of ANY clause of an if statement. Matching else problem –if no curly braces {} are used, this can occur –two ifs, but only one else. –Rule – the else ALWAYS matches the inner most if

Matching-Else Problem Example if (month == 4) if (day > 15) printf("Your taxes are late.\n"); else printf("File your taxes by 4/15.\n"); If month is NOT 4 –Nothing gets printed If month is 4 and day is 15 or less –File your taxes by 4/15 is printed If month is 4 and day is 16 or more –Your taxes are late is printed

Forgetting {} if (month == 4) printf(“It is close to tax time.\n”); printf(“Finish by the 15th.\n”); else printf(“It is not tax month.\n”); This is a syntax error Finish by the 15th would always print, and no statement is allowed to start with else. Curly braces for the if fix it.

Forgetting {} if (month == 4) printf(“It is close to tax time.\n”); else printf(“It is not tax month.\n”); printf(“Find something else to do.\n”); This is perfectly valid. But, the statement, “Find something else to do” will always print no matter what.

Difference between 1 if and separate ifs With one if statement, only one clause of statements can be executed With several separate if statements, one after another, there is the potential for multiple if statements to be executed

Example of separate ifs if (grade >= 90) –printf(“A\n”); if (grade >= 80) –printf(“B\n”); if (grade >= 70) –printf(“C\n”); if (grade >= 80) –printf(“D\n”); Else –printf(“F\n”);

One Last Note Order of Operations of && is greater than || Easiest to just use extra parentheses.