Unit 5

Decision Making & Branching

5.1 Decision making using simple if, if…else statement, nesting of if…else, else…if Ladder.

In conditional branching change in sequence of statement execution is depends upon the specified condition. Conditional statements allow programmer to check a condition and execute certain parts of code depending on the result of conditional expression. Conditional expression must be resulted into Boolean value. In C language, there are two forms of conditional statements:

1. If-----else statement: It is used to select one option between two alternatives

2. Switch statement: It is used to select one option between multiple alternative

• If Statements

This statement permits the programmer to allocate condition on the execution of a statement. If the evaluated condition found to be true, the single statement following the "if" is execute. If the condition is found to be false, the following statement is skipped. Syntax of the if statement is as follows

In the above syntax, “if” is the keyword and condition in parentheses must evaluate to true or false. If the condition is satisfied (true) then compiler will execute statement1 and then statement2. If the condition is not satisfied (false) then compiler will skip statement1 and directly execute statement2.

              if-----else statement

This statement permits the programmer to execute a statement out of the two statements. If the evaluated condition is found to be true, the single statement following the "if" is executed and statement following else is skipped. If the condition is found to be false, statement following the "if" is skipped and statement following else is executed. 

In this statement “if” part is compulsory whereas “else” is the optional part. For every “if” statement there may be or may not be “else” statement but for every “else” statement there must be “if” part otherwise compiler will gives “Misplaced else” error. 

Syntax of the “if----else” statement is as follows

In the above syntax, “if” and “else” are the keywords and condition in parentheses must evaluate to true or false. If the condition is satisfied (true) then compiler will execute statement1 and skip statement2. If the condition is not satisfied (false) then compiler will skip statement1 and directly execute statement2.

Nested if-----else statements :

Nested “if-----else” statements are used when programmer wants to check multiple conditions. Nested “if---else” contains several “if---else” a statement out of which only one statement is executed. Number of “if----else” statements is equal to the number of conditions to be checked. Following is the syntax for nested “if---else” statements for three conditions

In the above syntax, compiler first check condition1, if it trues then it will execute statement1 and skip all the remaining statements. If condition1 is false then compiler directly checks condition2, if it is true then compiler execute statement2 and skip all the remaining statements. If condition2 is also false then compiler directly checks condition3, if it is true then compiler execute statement3 otherwise it will execute statement 4.

Note:

If the test expression is evaluated to true,

• Statements inside the body of if are executed.

• Statements inside the body of else are skipped from execution.

If the test expression is evaluated to false,

• Statements inside the body of else are executed

• Statements inside the body of if are skipped from execution.

// Check whether an integer is odd or even

#include <stdio.h>

Int main() {

Int number;

Printf("Enter an integer: ");

Scanf("%d", &number);

// True if the remainder is 0

If  (number%2 == 0) {

Printf("%d is an even integer.",number);

}

Else {

Printf("%d is an odd integer.",number);

}

Return 0;

}

Program to relate two integers using =, > or < symbol

#include <stdio.h>

Int main() {

Int number1, number2;

Printf("Enter two integers: ");

Scanf("%d %d", &number1, &number2);

//checks if the two integers are equal.

If(number1 == number2) {

Printf("Result: %d = %d",number1,number2);

}

//checks if number1 is greater than number2.

Else if (number1 > number2) {

Printf("Result: %d > %d", number1, number2);

}

//checks if both test expressions are false

Else {

Printf("Result: %d < %d",number1, number2);

}

Return 0;

}

5.2 Switch statements, conditional operator, goto statement.

This statement permits the programmer to choose one option out of several options depending on one condition. When the “switch” statement is executed, the expression in the switch statement is evaluated and the control is transferred directly to the group of statements whose “case” label value matches with the value of the expression. Syntax for switch statement is as follows:

In the above, “switch”, “case”, “break” and “default” are keywords. Out of which “switch” and “case” are the compulsory keywords whereas “break” and “default” is optional keywords.

• “switch” keyword is used to start switch statement with conditional expression.
• “case” is the compulsory keyword which labeled with a constant value. If the value of expression matches with the case value then statement followed by “case” statement is executed.
• “break” is the optional keyword in switch statement. The execution of “break” statement causes the transfer of flow of execution outside the “switch” statements scope. Absence of “break” statement causes the execution of all the following “case” statements without concerning value of the expression.
• “default” is the optional keyword in “switch” statement. When the value of expression is not match with the any of the “case” statement then the statement following “default” keyword is executed.

Example: Program to spell user entered single digit number in English is as follows

Output

Enter a number

5

Five

1. Goto statement: “goto” statement is used to transfer the flow of program to any part of the program. The syntax of “go to” statement is as follows              

In the above syntax “goto” is keyword which is used to transfer the flow of execution to the label specified after it. Label is an identifier that is used to mark the target statement to which the control is transferred. The target statement must be labeled and the syntax is as follows

In the above syntax label name can be anything but it should be same as that of name of the label specified in “goto” statement, a colon must follow the label. Each labeled statement within the function must have a unique label, i.e., no two statements can have the same label.