Introduction

• Allow different sets of instructions to be executed depending on truth or falsity of alogical condition also called Branching
• How do we specify conditions?
• Using expressions
• non-zero value means condition is true
• value 0 means condition is false

• Usually logical expressions, but can be any expression
• The value of the expression will be used

The if Statement

Equality and Assignment Operators

• Dangerous error
• Does not ordinarily cause syntax errors
• Any expression that produces a value can be used in control structures
• Nonzero values are true, zero values are false
• Example:
if ( payCode = 4 )
printf( "You get a bonus!\n" );
Note:WRONG! Will always print the line

Multiple Statements within if

          #include<stdio.h>
          int main()
          {
            int num=19;
            if(num < 10)
            {	
              printf("Number is %d.\n",num);
              printf("The value is less than 10");
            }
            else
            {	
              printf("The value is greater than 10\n");
              printf("Number is %d.\n",num);
            }
            return 0;
          }
      

        Output:
        The value is greater than 10
        Number is 19.
        

The if-else Statement

      Illustration 4.1
          void main() {
          int marks;
          scanf("%d", &marks);
          if (marks >= 80)
            printf ("A") ;
          else if (marks >= 70)
            printf ("B") ;
          else if (marks >= 60)
            printf ("C") ;
          else printf ("Failed") ;
      }
      

Nested if-else

• It is possible to nest if-else statements,one within another
• All "if" statements may not be having the "else" part
Confusion??
• Rule to be remembered:
An "else" clause is associated with the closest preceding unmatched "if"

      Illustration 4.2
      int main () 
        {
        int a = 1;
        if( a < 10) 
        {
            if( a == 1) 
          {
              printf("Value of a is:%d\n",a);
            }
          else
          {
          printf("The value is greater than 100.");
          }
        }
        else
        {
        printf("The value is greater than 10.");
        }
        return 0;
      }
        

        Output:

        Value of a is:1
        

The Terniary Operator ?:

This makes use of an expression that is either non-0 or 0.
An appropriate value is selected,depending on the value of the expression

Syntax:-

Condition ? True Statement : False Statement

Note:if condition will true then true statement will be executed else false statement will be executed.

The switch statement

• An alternative to writing lots of if-else in some special cases
• This causes a particular group of statements to be chosen from several available groups based on equality tests only
• Uses switch statement and case labels

• Syntax

      switch (expression) {
      case const-expr-1: S-1
      case const-expr-2: S-2
      :
      case const-expr-m: S-m
      default: S
      }
  

• expression is any integer-valued expression
• const-expr-1, const-expr-2,..are any constant integer- valued expressions
  Values must be distinct
• S-1, S-2,...,S-m, S are statements/compound statements
• Default is optional, and can come anywhere (not necessarily at the end as shown)

Behaviour of switch

• expression is first evaluated
• It is then compared with const-expr-1,constexpr-2,...for equality in order
• If it matches any one, all statements from that point till the end of the switch are executed (including statements for default, if present)
• Use break statements if you do not want this (see example)
• Statements corresponding to default, if present,are executed if no other expression matches

Example

The break statement

• Used to exit from a switch or terminate from a loop
• With respect to "switch", the "break" statement causes a transfer of control out of the entire "switch" statement, to the first statement following the "switch" statement
• Break out of the loop body { }
• It can use with while, do while, for, switch,
• It does not work with if, else
• It Causes immediate exit from a while,do/while, for or switch structure
• Program execution continues with the first statement after the structure
• It Can be used with other statements also

Chapter 4 Quiz