# L4post - Previous Lecture: Branching (if, elseif, else,...

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± Previous Lecture: ± Branching ( if , elseif , else , end ) ± Relational operators ( < , >= , == , ~= , …, etc.) ± Today’s Lecture: ± Logical operators ± More branching— nesting ± Announcements: ± Project 1 (P1) due Thursday at 11pm ± Submit real .m files (plain text, not from a word processing software such as Microsoft Word) ± Discussion sections this week in the lab, UP B7 ± Register your clicker with CIT. Use the link on course website.

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September 8, 2009 Lecture 4 2 Consider the quadratic function q ( x ) = x 2 + bx + c on the interval [ L , R ] : ± Is the function strictly increasing in [ L , R ] ? ± Which is smaller , q ( L ) or q ( R ) ? ± What is the minimum value of q ( x ) in [ L , R ] ?
September 8, 2009 Lecture 4 3 % Which is smaller, q(L) or q(R)? qL= L*L + b*L + c; % q(L) qR= R*R + b*R + c; % q(R) if ( qL == qR ) disp(‘qleft and qright are equal’) elseif ( qL < qR ) disp(‘qleft is smaller’) else disp(‘qright is smaller’) end

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September 8, 2009 Lecture 4 4 The if construct if boolean expression1 statements to execute if expression1 is true elseif boolean expression2 statements to execute if expression1 is false but expression2 is true : else statements to execute if all previous conditions are false end C a n h v e y u m b r of l s i f c
September 8, 2009 Lecture 4 5 Consider the quadratic function q ( x ) = x 2 + bx + c on the interval [ L , R ] : What if you only want to know if q ( L ) is close to q ( R ) ?

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September 8, 2009 Lecture 4 6 % Is q(L) close to q(R)? tol= 1e-4; % tolerance qL= L*L + b*L + c; qR= R*R + b*R + c; if ( abs(qL-qR) < tol ) disp(‘qleft and qright similar’) end N a m e n i p o r t d de f w it h c !
September 8, 2009 Lecture 4 8 Can have if without else if boolean expression statements to execute if expression is true end

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September 8, 2009 Lecture 4 9 Do these two fragments do the same thing? % given x, y if x>y disp(‘alpha’) else disp(‘beta’) end % given x, y if x>y disp(‘alpha’) end if y>=x disp(‘beta’) end A: yes B: no
September 8, 2009 Lecture 4 10 The if construct if boolean expression1 statements to execute if expression1 is true elseif boolean expression2 statements to execute if expression1 is false but expression2 is true : else statements to execute if all previous conditions are false end C a n h v e y u m b r of l s i f c t os on ls

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September 8, 2009 Lecture 4 12 Things to know about the if construct ± At most one branch of statements is executed ± There can be any number of elseif clauses ± There can be at most one else clause ± The clause
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## This note was uploaded on 03/06/2010 for the course CS 9339 taught by Professor Gries during the Fall '09 term at Cornell University (Engineering School).

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L4post - Previous Lecture: Branching (if, elseif, else,...

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