C Programming - The ELSE If Ladder

When a series of many conditions have to be checked we may use the ladder else if statement which takes the following general form.

This construct is known as if else construct or ladder. The conditions are evaluated from the top of the ladder to downwards. As soon on the true condition is found, the statement associated with it is executed and the control is transferred to the statement – x (skipping the rest of the ladder. When all the condition becomes false, the final else containing the default statement will be executed.

Example program using If else ladder to grade the student
#include <stdio.h> //include the standard stdio.h header file
void main () //start the function main
{
   int marks; //variable declaration
 
   printf ("Enter marks\n"); //message to the user
   scanf ("%d", &marks); //read and store the input marks. 
 
   if (marks <= 100 && marks >= 70) //check whether marks is less than 100 or greater than 70 
         printf ("\n Distinction");  //print Distinction if condition is True
   else if (marks >= 60) //else if the previous condition fails Check
         printf("\n First class"); //whether marks is > 60 if true print Statement
   else if (marks >= 50) //else if marks is greater than 50 print
         printf ("\n second class"); //Second class
   else if (marks >= 35) //else if marks is greater than 35 print
         printf ("\n pass class"); //pass class
   else
         printf ("Fail"); //If all condition fail apply default condition print Fail
}

The above program checks a series of conditions. The program begins from the first if statement and then checks the series of conditions it stops the execution of remaining if statements whenever a condition becomes true.

In the first If condition statement it checks whether the input value is lesser than 100 and greater than 70. If both conditions are true it prints distinction. Instead if the condition fails then the program control is transferred to the next if statement through the else statement and now it checks whether the next condition given is whether the marks value is greater than 60 If the condition is true it prints first class and comes out of the If else chain to the end of the program on the other hand if this condition also fails the control is transferred to next if statements program execution continues till the end of the loop and executes the default else statement fails and stops the program.

The Switch Statement:

Unlike the If statement which allows a selection of two alternatives the switch statement allows a program to select one statement for execution out of a set of alternatives. During the execution of the switch statement only one of the possible statements will be executed the remaining statements will be skipped. The usage of multiple If else statement increases the complexity of the program since when the number of If else statements increase it affects the readability of the program and makes it difficult to follow the program. The switch statement removes these disadvantages by using a simple and straight forward approach.

The general format of the Switch Statement is :

When the switch statement is executed the control expression is evaluated first and the value is compared with the case label values in the given order. If the label matches with the value of the expression then the control is transferred directly to the group of statements which follow the label. If none of the statements matches then the statement against the default is executed. The default statement is optional in switch statement in case if any default statement is not given and if none of the condition matches then no action takes place in this case the control transfers to the next statement of the if else statement.

A program to stimulate the four arithmetic operations using switch
#include <stdio.h> 
void main () 
{  
   int num1, num2, result; 
   char operator;
 
   printf ("Enter two numbers"); 
   scanf ("%d %d", &num1, &num2); 
   printf ("Enter an operator"); 
   scanf ("%c", &operator); 
 
   switch (operator) 
   {
       case '+': 
          result = num1 + num2; 
          break; 
       case '-': 
          result = num1 - num2; 
          break; 
       case '*': 
          result = num1 * num2; 
          break; 
       case '/': 
          if (num2 != 0) 
             result = num1 / num2; 
          else
          {        
             printf ("warning : division by zero \n");
             result = 0;
          }
          break;
       default: 
          printf ("\n unknown operator");
          result = 0;
          break; 
   }
   printf ("%d", result); 
}

In the above program the break statement is need after the case statement to break out of the loop and prevent the program from executing other cases.

The GOTO statement:

The goto statement is simple statement used to transfer the program control unconditionally from one statement to another statement. Although it might not be essential to use the goto statement in a highly structured language like C, there may be occasions when the use of goto is desirable.

Syntax

The goto requires a label in order to identify the place where the branch is to be made. A label is a valid variable name followed by a colon.

The label is placed immediately before the statement where the control is to be transformed. A program may contain several goto statements that transferred to the same place when a program. The label must be unique. Control can be transferred out of or within a compound statement, and control can be transferred to the beginning of a compound statement. However the control cannot be transferred into a compound statement. The goto statement is discouraged in C, because it alters the sequential flow of logic that is the characteristic of C language.

A program to find the sum of n natural numbers using goto statement
#include <stdio.h> //include stdio.h header file to your program
main () //start of main
{
     int n, sum = 0, i = 0; // variable declaration
     printf ("Enter a number"); // message to the user
     scanf ("%d", &n); //Read and store the number
     loop: i++; //Label of goto statement
     sum += i; //the sum value in stored and I is added to sum 
     if (i < n) goto loop; //If value of I is less than n pass control to loop
     printf ("\n sum of %d natural numbers = %d", n, sum);
     //print the sum of the numbers & value of n
}

The ELSE If Ladder

The Switch Statement:

The GOTO statement:

Tags