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Computer Programming CS F111. Vishal Gupta Department of Computer Science and Information Systems Birla Institute of Technology and Science Pilani Campus, Pilani . Agenda :. Expression Evaluation: Precedence & Associativity. Precedence and Associativity ?.

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Computer programming cs f111
Computer ProgrammingCS F111

Vishal Gupta

Department of Computer Science and Information Systems

Birla Institute of Technology and Science

Pilani Campus, Pilani


Computer programming cs f111

Agenda:

Expression Evaluation: Precedence & Associativity


Precedence and associativity
Precedence and Associativity?

  • Operators have rules that are used to determine how expressions are evaluated.

  • Precedence and associativity deal with the evaluation order within expressions.

  • Precedencerules specify the order in which operators of different precedence level are evaluated.

  • Associativityrules decides the order in which multiple occurrences of the same level operator are applied.


Rules of evaluation of expression
Rules of Evaluation of Expression

  • First, parenthesized sub expression from left to right are evaluated.

  • If parentheses are nested, the evaluation begins with the innermost sub expression.

  • The precedence rule is applied in determining the order of application of operators in evaluating sub-expressions.

  • The associativity rule is applied when two or more operators of the same precedence level appear in a sub expression.


Examples evaluate the following expressions
Examples: Evaluate the following expressions

1) z = 2*3/4+4/4+8-2+5/7

z = ??

2) y = 4/5*6+2/7+4

y = ??

3) Let inta,b;

float c,d;

a=5;b=7;

c=4.0;d=3.0;

Then compute

x = a/b*(c+d)/a-b+c/d


Example

Example

What is the output of the following piece of code ??

#include <stdio.h>

int main (void)

{

int a, b=21, c=7;

a = ++c – b-- % 5;

printf (“Value of a = %d, b = %d, c = %d”,a, b, c);

}

Priority can be overruled by parenthesis. With this expression inside parenthesis are evaluated first so

(1+2)*3 gives 9