Use flowcharts and procedures to describe decision-making concepts in C

The following is the decision statement-

• Simple- if statement
• if-else statement
• Nested-if else statement
• else – ifladder
• switch statement

Simple – if statement

The “if” keyword is used to execute a set of statements when a logical condition is true.

Syntax

if (condition){
   Statement (s)
}

Example

The following example checks whether a number is greater than 50.

#include<stdio.h>
main (){
   int a;
   printf (&ldquo;enter any number:</p><p>&rdquo;);
   scanf (&ldquo;%d&rdquo;, &a);
   if (a>50)
      printf (&ldquo;%d is greater than 50&rdquo;, a);
}

Output

1) enter any number: 60
60 is greater than 50 .
2) enter any number 20
no output

if else statement

if else statement accepts True or False conditions.

Syntax

if (condition){
   True block statement(s)
}
else{
   False block statement(s)
}

Flowchart

Example

The following is a program to check odd and even numbers−

#include<stdio.h>
main (){
   int n;
   printf (&ldquo;enter any number:</p><p>&rdquo;);
   scanf (&ldquo;%d&rdquo;, &n);
   if (n%2 ==0)
      printf (&ldquo;%d is even number&rdquo;, n);
   else
      printf( &ldquo;%d is odd number&rdquo;, n);
}

Output

1) enter any number: 10
10 is even number

Nested if - else statement

Here the "if" is placed inside another if (or) else-

Syntax

if (condition1){
   if (condition2)
      stmt1;
   else
      stmt2;
   }
   else{
      if (condition3)
         stmt3;
      else
         stmt4;
   }

Flow chart

Example

The following example is to print the largest 3 digits of the given number.

#include<stdio.h>
main (){
   int a,b,c;
   printf (&ldquo;enter 3 numbers&rdquo;);
   scanf (&ldquo;%d%d%d&rdquo;, &a, &b, &c);
   if (a>b){
      if (a>c)
         printf (&ldquo;%d is largest&rdquo;, a);
      else
         printf (&ldquo;%d is largest&rdquo;, c);
   } else {
      if (b>c)
         printf (&ldquo;%d is largest&rdquo;, b);
      else
         printf (&ldquo;%d is largest&rdquo;, c);
   }
}

Output

enter 3 numbers = 10 20 30
30 is largest

Else – if ladder

It is a multi-way decision condition.

Syntax

if (condition1)
   stmt1;
else if (condition2)
   stmt2;
   - - - - -
   - - - - -
else if (condition n)
   stmt n;
else
   stmt x;

Flow chart

Example

The following example finds the roots of a quadratic equation-

#include <math.h>
main (){
   int a,b,c,d;
   float r1, r2
   printf ("enter the values a b c");
   scanf (&ldquo;%d%d%d&rdquo;, &a, &b, &c);
   d= b*b &ndash; 4*a*c ;
   if (d>0){
      r1 = (-b+sqrt(d)) / (2*a);
      r2 = (-b-sqrt(d)) / (2*a);
      printf (&ldquo;root1 ,root2 =%f%f&rdquo;, r1, r2);
   }
   else if (d== 0){
      r1 = -b / (2*a);
      r2 = -b/ (2*a);
   printf (&ldquo;root1, root2 = %f%f&rdquo;, r1, r2);
   }
   else
      printf ("roots are imaginary&rdquo;);
}

Output

1) enter the values of a b c : 1 4 3
Root 1 = -1
Root 2 = -3

Switch statement

It helps to select one from multiple decisions.

Grammar

switch (expression){
   case value1 : stmt1;
      break;
   case value2 : stmt2;
      break;
   - - - - - -
   default : stmt – x;
}

Grammar

Example

#include<stdio.h>
main (){
   int n;
   printf (&ldquo;enter a number&rdquo;);
   scanf (&ldquo;%d&rdquo;, &n);
   switch (n){
      case 0 : printf (&ldquo;zero&rdquo;)
         break;
      case 1 : printf (&lsquo;one&rdquo;);
         break;
      default : printf (&lsquo;wrong choice&rdquo;);
   }
}

Output

enter a number
1
One

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