{"id":799,"date":"2022-06-22T10:19:10","date_gmt":"2022-06-22T04:49:10","guid":{"rendered":"https:\/\/pythonarray.com\/?p=799"},"modified":"2022-06-28T15:24:31","modified_gmt":"2022-06-28T09:54:31","slug":"python-programming-decision-making","status":"publish","type":"post","link":"https:\/\/pythonarray.com\/python-programming-decision-making\/","title":{"rendered":"Python Programming &#8211; Decision Making"},"content":{"rendered":"<h2>Python Programming &#8211; Decision Making<\/h2>\n<p>Decision-making is done with a conditional statement which allows selecting one or another execution path in a program. It causes to execution of a particular block of statements after the evaluation of a given conditional expression. In other words, appropriate action is preceded by the evaluation of a test condition to either true or false. Table 4.1. depicts a list of decision-making control structures supported by Python language. Now, we will learn each of the control structures in detail.<\/p>\n<table>\n<tbody>\n<tr>\n<td width=\"180\">\n<p style=\"text-align: center;\"><strong>Statement<\/strong><\/p>\n<\/td>\n<td width=\"444\">\n<p style=\"text-align: center;\"><strong>Description<\/strong><\/p>\n<\/td>\n<\/tr>\n<tr>\n<td width=\"180\">if statement<\/td>\n<td width=\"444\">An if statement consists of an expression (which results in either true or false) followed by a block of one or more statements.<\/td>\n<\/tr>\n<tr>\n<td width=\"180\">if..else statement<\/td>\n<td width=\"444\">An if statement followed by an else statement, which executes when the boolean expression turns false.<\/td>\n<\/tr>\n<tr>\n<td width=\"180\">if&#8230;elif. ..else statement<\/td>\n<td width=\"444\">An if statement can be followed by an optional elif and else statements, where elif is accompanied with a test condition similar to if statement.<\/td>\n<\/tr>\n<tr>\n<td width=\"180\">nested if statement<\/td>\n<td width=\"444\">It contains if statement inside another if or else if statement(s).<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p><strong>Note:<\/strong><br \/>\nPython programming language assumes any non\u00aczero and non-null values as TRUE, and if it is either zero or null, then it is assumed as FALSE value.<\/p>\n<ul>\n<li><a href=\"https:\/\/pythonarray.com\/python-programming-conditional-and-iterative-statements\/\">Python Programming \u2013 Conditional and Iterative Statements<\/a><\/li>\n<li><a href=\"https:\/\/pythonarray.com\/python-programming-notion-of-iterating-computation-loops\/\">Python Programming \u2013 Notion Of Iterating Computation (Loops)<\/a><\/li>\n<li><a href=\"https:\/\/pythonarray.com\/python-programming-if-elif-else-statements\/\">Python Programming \u2013 If-Elif-Else Statements<\/a><\/li>\n<\/ul>\n<p><strong>Python if Statement<\/strong><\/p>\n<p>The Python if statement can execute either a simple or compound statement depending on the result of the expression. The syntax of Python if statement is given as follows:<\/p>\n<table>\n<tbody>\n<tr>\n<td width=\"623\">if test condition:<br \/>\nstatement(s)<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p>Here, the program evaluates the test condition (expression) and will execute statement(s) only if the test expression evaluates to True. If the test expression is False, the statement(s) does not get executed. As we know that, in Python, indentation is necessary. The beginning of a block is always marked with the indented statement and the closing of a block is marked by the unindented statement. Therefore, the body of the if statement is indicated by the indentation. The body starts with an indentation and the first unindented line marks the end. Python interprets non-zero values as True. None and 0 are interpreted as False. The flow diagram of the if statement is given in Fig. 4.1.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone size-full wp-image-803\" src=\"https:\/\/pythonarray.com\/wp-content\/uploads\/2021\/05\/Python-Programming-Decision-Making-chapter-3-img-1.png\" alt=\"Python Programming - Decision Making chapter 3 img 1\" width=\"239\" height=\"279\" \/><\/p>\n<p>Code: 4.1 Illustration of if statement to determine whether a number is even.<\/p>\n<table>\n<tbody>\n<tr>\n<td width=\"623\"># This program determines whether a number is even using if statement<\/p>\n<p>number=input(&#8216;Enter a number:&#8217;)<br \/>\nnumber=int(number)<br \/>\nif number%2==0:<br \/>\nprint(&#8216;Number is even&#8217;)<br \/>\nprint(&#8216;out of if block&#8217;)<\/td>\n<\/tr>\n<tr>\n<td width=\"623\">Output 1:<br \/>\nEnter a number: 12<br \/>\nNumber is even<br \/>\nOut of if blockOutput 2:<br \/>\nEnter a number: 7<br \/>\nOut of if block<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p>The programming example of the if statement \u201cto determine whether a number is even\u201d is given in Code 4.1. In this code, number%2 == 0 is the test expression. The body of if is executed only if this evaluates to True. When a user enters 12, the test expression is true then the indented statement under if statement gets executed. When a user enters 7, the test expression is false then the indented statement under if is skipped. The unindented print() statement falls outside of the if block. Hence, it is executed regardless of the test expression.<\/p>\n<p>We can see this in our two outputs above. Another example of if a statement is given in Code 4.2, the program code determines whether a number is positive. It is explicable from the code that if the user inputs the value of the number variable 5 then the \u201cIt is a positive number\u201d message will be displayed along with the \u201cout of if block\u201d message. However, when the user inputs a &#8211; 5 then if the statement evaluates to false, and \u201cOut of if block\u201d message is displayed bypassing the indented statement associated with the if statement.<\/p>\n<p>Code 4.2. Illustration of if statement to determine whether a number is positive.<\/p>\n<table>\n<tbody>\n<tr>\n<td width=\"623\"># This program determines whether a number is positive using if statement.<br \/>\nnumber=input(&#8216;Enter a number:&#8217;)<br \/>\nnumber=int(number)<br \/>\nif number&gt;0:<br \/>\nprint(&#8216;It is a positive number&#8217;)<br \/>\nprint(&#8216;Out of if block&#8217;)<\/td>\n<\/tr>\n<tr>\n<td width=\"623\">Output 1:<br \/>\nEnter a number: 5<br \/>\nIt is a positive number<br \/>\nOut of if blockOutput 2:<br \/>\nEnter a number: -5<br \/>\nOut of if block<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p><strong>Python if-else Statement<\/strong><\/p>\n<p>The if statement executes a simple or compound statement when the test expression provided in the if statement evaluates to true. However, as in the above Code 4.1 and Code 4.2, we see that what if the test expression evaluates to false. Python language provides the solution for this by the if-else statement. An else statement contains the block of code that gets executed if the conditional test expression in the if statement evaluates to 0 or a false value. The else statement is an optional statement and there could be at most only one else statement following if. The syntax of if&#8230;else statement is given as under<\/p>\n<table>\n<tbody>\n<tr>\n<td width=\"623\">if test condition:<br \/>\nstatement(s)<br \/>\nelse:<br \/>\nstatement(s)<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p>As shown in the syntax, initially test condition associated with if is evaluated, if it evaluates to true then statements following if block is executed. If the test condition evaluates to false then the statements associated with else block are executed. The flow diagram of if&#8230;else construct is represented in Fig. 4.2.<\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"alignnone wp-image-804 size-full\" src=\"https:\/\/pythonarray.com\/wp-content\/uploads\/2021\/05\/Python-Programming-Decision-Making-chapter-3-img-2.png\" alt=\"Python Programming - Decision Making chapter 3 img 2\" width=\"382\" height=\"273\" srcset=\"https:\/\/pythonarray.com\/wp-content\/uploads\/2021\/05\/Python-Programming-Decision-Making-chapter-3-img-2.png 382w, https:\/\/pythonarray.com\/wp-content\/uploads\/2021\/05\/Python-Programming-Decision-Making-chapter-3-img-2-300x214.png 300w\" sizes=\"(max-width: 382px) 100vw, 382px\" \/><\/p>\n<p>The programming example of if&#8230;else construct is given in Code 4.3. The program determines whether a number is even or odd. In the previous example, we see that when the test expression number%2==0 evaluates to false then the \u201cOut of if block\u201d statement is executed. However, by using if.. .else construct the output is displayed as \u201cNumber is odd\u201d for a false test condition. Similarly, in the case of another program, where it is determined that whether a number is positive or not. For a false condition, the else statement block is executed, which displays \u201cIt is a negative number\u201d, as shown in Code 4.4.<\/p>\n<p>Code: 4.3. To determine whether a number is even or odd using if&#8230;else construct.<\/p>\n<table>\n<tbody>\n<tr>\n<td width=\"623\">#This program determines whether a number is even or odd using if&#8230;else construct<\/p>\n<p>number=input(&#8216;Enter a number:&#8217;)<br \/>\nnumber=int(number)<br \/>\nif number%2==0:<br \/>\nprint(&#8216;Number is even&#8217;)<br \/>\nelse:<br \/>\nprint(&#8216;Number is odd&#8217;)<\/td>\n<\/tr>\n<tr>\n<td width=\"623\">Output 1:<br \/>\nEnter a number: 12<br \/>\nNumber is evenOutput 2:<br \/>\nEnter a number: 7<br \/>\nNumber is odd<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p>Code 4.4. To determine whether a number is positive or negative using if&#8230;else construct.<\/p>\n<table>\n<tbody>\n<tr>\n<td width=\"623\"># This program determines whether a number is positive or negative using if&#8230;else statement<\/p>\n<p>number=input(&#8216;Enter a number:&#8217;)<br \/>\nnumber=int(number)<br \/>\nif number&gt;0:<br \/>\nprint(&#8216;It is a positive number&#8217;)<br \/>\nelse:<br \/>\nprint(&#8216;It is a negative number&#8217;)<\/td>\n<\/tr>\n<tr>\n<td width=\"623\">Output 1:<br \/>\nEnter a number: 7 It is a positive number<br \/>\nOutput 2:<br \/>\nEnter a number: -9 It is a negative number<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p><strong>Python if&#8230;elif&#8230;else<\/strong><\/p>\n<p>The elif statement allows you to check multiple expressions for true and execute a block of code as soon as one of the conditions evaluates to true. It is similar to if&#8230;else if&#8230;else construct of C, C++, and Java. Similar to the else, the elif statement is optional. However, unlike else, there can be an arbitrary number of elif statements following an if. Like, if statement elif is associated with a test condition. The syntax of if&#8230;elif&#8230;else is given as under:<\/p>\n<table>\n<tbody>\n<tr>\n<td width=\"623\">if test condition:<br \/>\nstatement(s)<br \/>\nstatement(s)<br \/>\nelse<br \/>\nstatement(s)<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p>As shown in the syntax, If the test condition for if evaluates to false, it checks the condition of the next elif block and so on. If all the conditions are false, a block of else is executed. Only one of the several if&#8230;elif&#8230;else blocks is executed according to the condition. The flow diagram of if&#8230;elif&#8230; else is given in Fig. 4.3.<\/p>\n<p>Code:4.5. To determine whether a number is positive, negative or zero using if.. .elif.. .else construct<\/p>\n<table>\n<tbody>\n<tr>\n<td width=\"623\"># This program determines whether a number is positive, negative or zero<br \/>\n# by using if&#8230;elif&#8230;else statementnumber=input(&#8216;Enter a number:&#8217;)<br \/>\nnumber=int(number)<br \/>\nif number&gt;0:<br \/>\nprint(&#8216;Number is positive&#8217;)<br \/>\nelif number==0:<br \/>\nprint(&#8216;Number is zero&#8217;)<br \/>\nelse:<br \/>\nprint(&#8216;Number is negative&#8217;)<\/td>\n<\/tr>\n<tr>\n<td width=\"623\">Output 1<\/p>\n<p>Enter a number: 5<br \/>\nNumber is positive<\/td>\n<\/tr>\n<tr>\n<td width=\"623\">Output 2<\/p>\n<p>Enter a number: -5<br \/>\nNumber is negative<\/td>\n<\/tr>\n<tr>\n<td width=\"623\">Output 3<\/p>\n<p>Enter a number: 0<br \/>\nNumber is zero<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p><strong>Python Nested if Statements<\/strong><\/p>\n<p><span style=\"font-size: inherit; letter-spacing: 0px;\">There may be a situation when the programmer wants to check for another condition after a condition resolves to true. In such a situation, the nested if construct can be used. In a nested, if construct, we can have an if&#8230;elif&#8230;else construct inside another if&#8230;elif&#8230;else construct and so on. The syntax of nested if construct is given as follows:<\/span><\/p>\n<table>\n<tbody>\n<tr>\n<td width=\"623\">if test condition:<br \/>\nstatement(s) if test condition:<br \/>\nstatement(s)<br \/>\nelif test condition:<br \/>\nstatement(s)<br \/>\nelse<br \/>\nstatement(s)<br \/>\nelif test condition:<br \/>\nstatement(s)<br \/>\nelse<br \/>\nstatement(s)<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p>The program representing the significance of nested if is given in Code:4.6. When the user inputs the value of number=5 then the condition number&gt;=0 becomes true and control goes inside the nested if block, where it checks for number=0 test condition, which becomes false. Then else part associated with the nested if is executed and the result is displayed as \u201cPositive number\u201d. Similarly, in the second output when the user inputs number=0 the \u201cZero\u201d message is displayed and in the third output, we see that by entering a negative number the outer if the condition becomes false and it&#8217;s associated else part is executed, which displays \u201cNegative number\u201d.<\/p>\n<p>Code:4.6. To determine whether a number is positive, negative or zero using nested if statements.<\/p>\n<table>\n<tbody>\n<tr>\n<td width=\"623\"># This program input a number and determines whether it is positive, negative or zero using<br \/>\n# nested if statementsnumber= input(&#8216;Enter a number:&#8217;)<br \/>\nnumber=int(number)<br \/>\nif number&gt;=0:<br \/>\nif number == 0:<br \/>\nprint(&#8216;Zero&#8217;)<br \/>\nelse:<\/td>\n<\/tr>\n<tr>\n<td width=\"623\">\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Print (\u2018positive number\u2019)<\/p>\n<p>Else:<\/p>\n<p>Print (\u2018Negative number\u2019)<\/td>\n<\/tr>\n<tr>\n<td width=\"623\">Output 1<br \/>\nEnter a number: 5<br \/>\nPositive number<\/td>\n<\/tr>\n<tr>\n<td width=\"623\">Output 2<br \/>\nEnter a number: 0<br \/>\nZero<\/td>\n<\/tr>\n<tr>\n<td width=\"623\">Output 3<br \/>\nEnter a number: -10<br \/>\nNegative number<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<p><a href=\"https:\/\/pythonarray.com\/python-tutorial\/\">Python Tutorial<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"<p>Python Programming &#8211; Decision Making Decision-making is done with a conditional statement which allows selecting one or another execution path in a program. It causes to execution of a particular block of statements after the evaluation of a given conditional expression. In other words, appropriate action is preceded by the evaluation of a test condition&hellip;<\/p>\n","protected":false},"author":2,"featured_media":2972,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"spay_email":"","footnotes":""},"categories":[2],"tags":[],"jetpack_featured_media_url":"https:\/\/pythonarray.com\/wp-content\/uploads\/2021\/05\/Python-Programming-Decision-Making.png","jetpack-related-posts":[{"id":819,"url":"https:\/\/pythonarray.com\/python-programming-control-structures\/","url_meta":{"origin":799,"position":0},"title":"Python Programming - Control Structures","date":"June 22, 2022","format":false,"excerpt":"Python Programming - Control Structures Generally, a program is executed in a sequence normally from top to bottom. 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