What is Decision Making & Branching? Explain decision making & branching statements in ‘C’?

C program is a set of statements which are normally executed sequentially in the order in which they appear. In some situations we may have to change the order of execution of statements based on certain conditions, or repeat a group of statements until certain specified conditions are met. C language possesses such decision making capabilities by supporting the following statements. 1. if statement.                                  2. Switch statement                         3. Conditional operator statement.            4. goto statement These statements control the flow of execution of a program. That’s why there are also called as control statements. These statement tests the condition basing on the result make a decision to execute the statements. If statement:– The if statement is a powerful decision making statement & is used to control the flow of execution of statements. Ex:– if (test expression) It allows the computer to evaluate the exp first and then depending on whether the value of the exp is true or false, it transfers the control to a particular statement. The if statement may be implemented in different forms depending on the complexity of conditions to be tested. The different forms are: 1. simple if statement                                                 2. If….. else statement.        3. nested if ….else statement.                               4.else if ladder 1. simple if statement :–  The general form of a simple if statement is if (test expression) { Statements block; } Statement–X; Flow chart The statement may be a simple statement or a group of statements. If the test exp is true, the statement block will be executed. Otherwise the statement block will be skipped & the execution will jump to the statement x when the condition is true both the statement block & the statement –x are executed in sequence. Ex:– if (category = =  sports) { Marks = marks+bonus; } printf (“f”, marks); 2. The if…else statement: It is an extension of the simple if. The general form is if(test expression) { true–block statements } else { False–block statements } Statement–x; Flow Chart If the test exp. is true , then the true block statements, immediately following the if statements are executed otherwise, the false–block statements are executed. In either case, either true–block or false–block will be executed, not both. In both cases, the control is transferred subsequently to the statement. Ex:– if (cose==1) Boy=boy+1; Else girl =girls+1; - - -  - - - - - - 3. nesting of  if ….. else statement:– When a series of decisions are involved, we may have to use more than one if…… else statement in nested form as shown below. Syntax:– if (test condition1) {             Statement1 } else { Statement2 } } else { Statement=3; } Statement = x; If the con1 is false, the statement 3 will be executed otherwise it continues to perform the 2nd test. If the con2 is true, the statement1will evaluated & then the control is transferred to the statement. Flow Chart 4.the else if ladder:  There is another way of putting if’s together when multipath decisions are involved. A multipath decision is a chain of if’s in which the statement associated with each else is an if. The general form is : Syntax: if (con1)             Statement–1;             else if(con–2)             statement–2             else if(con–3)             statement–3             else if(con.n)             statement–n             else             default–statement;             statement ; This construction is known as the else if ladder. The conditions are evaluated the top, downward as soon as a tree con is found, the statement associated with it is executed & the control is transferred  to the statement–x (skipping the rest of the ladder). When all the n conditions become false then the final else containing the default statement will be executed. Flow chart  Ex:–  If(code==1) Colour =”red”; else if (code = =2) colour=”green”; else if (code==3) colour=”while”; else colour = “yellow”; 2. The switch statement:–  C has a built–in multiway decision statement known as a switch. The switch statement tests the value of a given variable (or exp) against a list of case values & when a match is found , a block of statements announced with that case is executed. The general form is Syntax: switch(expression) { case value–1: block–1; break; case value–2: block–2; break; ---- --- default: default–block;             break; } Statement–x; The expression is an integer expression or characters. value–1, value–2….. are constants (or) constants expressions and are known as case labels. Each of these values should be unique with in a switch statement. block–1, block–2,….. are statement list & may contain 0 or more statements. There is no need to put braces around blocks. Note that case labels end with a colon(:) When the switch is executed, the value of the exp is successfully compared against the values value–1, value–2,…… If a case is found whose value matches with the value of the exp, then the block of statements that follow the case are executed. The break statement at the end of each block signals the end of a particular case and causes an exit from the switch statement transforming the control to the statement x following the switch. The default is an optional case. When present, it will be executed if the value of the exp. does not present no action takes place if all matches  fail & the control goes to the statement . Flow Chart Ex:–switch(op) { case 1: printf(“one”); break; case 2: printf(“two”); break; . . . default: printf(“not entered a digit”); } 3. The ?: operator:– Conditional op is useful for making 2–way decisions. This op is a combination of ? and :, & takes 3 operands. The general form is : Syntax:– conditional exp?exp–1:exp–2 The conditional exp. is evaluated first. It the result is nonzero, exp–1 is evaluated & its value is returned. Ex:– if(a>b) big=a; else big=b; can be written as big=(a>b)?a:b 4.Goto statement :– C supports the goto statement to branch unconditionally from one point to another in the program. The goto requires a label in order to identify the place where the branch is to be made. A label is any valid variable name, & must be followed by a colon. The label is placed immediately before the statement where the control is to be transferred. The general forms of goto & label statements are : Syntax:         The label cab be anywhere in the program either before or after the goto label; statement. If the label: is before the statement goto label; a loop will be formed & some statements will be executed repeatedly. Such a jump is known as a backward jump. On the other hand, if the label: is placed after the goto label; some statements will be skipped & the jump is known as forward jump.