Basics of Control Statement in C Languages

Subject: Programming In C Language C. P. Divate

CONTROL STATEMENTS C language supports the following statements known as control or decision making statements. 1. if statement 2. if…..else statement 3. Nesting of if…..else statement 4. if ……else ladder 5. switchstatement 6. conditional operatorstatement 7. Go tostatement

IF( ) STATEMENT  if statement is the most simple decision making statement.  It is used to decide whether a certain statement or block of statements will be executed or not.  i.e if a certain condition is true then a block of statement is executed otherwise not.  Syntax: if(condition) { // Statements to execute if // condition is true }  Example: if(bank balance is zero) Borrow money

IF( ) STATEMENT  Here, condition after evaluation will result either true or false.  if statement condition results in boolean values.  if the value is true then it will execute the block of statements below it otherwise not.  If we do not provide the curly braces ‘{‘ and ‘}’ after if(condition) then by default if statement will consider the first immediately below statement to be inside its block.

IF( ) STATEMENT Example // C program to illustrate If () #include <stdio.h> int main() { int i = 10; if (i > 15) { printf("10 is less than 15"); } printf("I am Not in if"); } Output: I am Not in if #include <stdio.h> int main() { int x = 20; int y = 22; if (x<y) { printf("Variable x is less than y"); } } Output1: Variable x is less than y

IF( ) STATEMENT Example Output1: Enter a number:4 4 is positive number // C program to check that no is positive #include<stdio.h> int main() { int number=0; printf("Enter a number:"); scanf("%d",&number); if(number >= 0) { printf("%d is positive number",number); } } Output1: Enter a number: -10

IF( ) STATEMENT Example // C program to check that no is even #include<stdio.h> int main() { int number=0; printf("Enter a number:"); scanf("%d",&number); if(number%2==0) { printf("%d is even number",number); } } Output1: Enter a number:4 4 is even number Output2: Enter a number:5

IF( ) STATEMENT Example // C program to check that no is divisible by 7 #include<stdio.h> int main() { int number=0; printf("Enter a number:"); scanf("%d",&number); if(number % 7==0) { printf("%d is divisible by 7",number); } } Output1: Enter a number:49 49 is divisible by 7 Output2: Enter a number:55

IF( ) STATEMENT Example // C to calculate fine in library #include<stdio.h> int main() { int days; float fine=0; printf("Enter no of days:"); scanf("%d",&days); if(days >=8) { fine=(days-8) * 2; } printf(“Fine = %f for Total days=%d”, fine, (days-8)); } Output1: Enter no of days:10 Fine = 4 for Total days=2 Output1: Enter no of days:7 Fine = 0 for Total days= -1

Multiple IF( ) STATEMENT Example // C Example of multiple if statements #include <stdio.h> int main() { int x, y; printf("enter the value of x:"); scanf("%d", &x); printf("enter the value of y:"); scanf("%d", &y); if (x>y) { printf("x is greater than yn"); } if (x<y) { printf("x is less than yn"); } Output1: enter the value of x:30 enter the value of y:20 x is greater than y End of Program Output2: enter the value of x:20 enter the value of y:20 x is equal to y End of Program if (x==y) { printf("x is equal to yn"); } printf("End of Program"); return 0; }

IF( ) STATEMENT Home work Example  Write a C program to check income is greater than 30000  Write a C program to calculate income_tax if income is greater than 30000 (formula income_tax=30 % of income)  Calculate result of student based on following conditions. if percentage < 35 then fail if percentage >= 35 then pass

IF( ) … else ….STATEMENT  if statement is the decision making statement.  An if statement can be followed by an optional else statement, which executes when the Boolean expression is false.  i.e if a certain condition is true then a block of statement is executed otherwise else block statement is executed.  Syntax: if (condition) { // block of code if condition is true } else { // block of code if condition is false }

 Here, condition after evaluation will result either true or false.  if statement condition results in boolean values.  if the value is true then it will execute the true block of if statements below it otherwise it will execute the false block(else block of if statements . IF( ) … else ….STATEMENT

IF( ) … else ….STATEMENT Example

IF( ) … else ….STATEMENT Example // C program to check given number is odd or even number #include<stdio.h> int main() { int number=0; printf("enter a number:"); scanf("%d",&number); if(number%2==0) { printf("%d is even number",number); } else { printf("%d is odd number", number); } printf(“End of Program"); } Output1: Enter a number:4 4 is even number Output2: Enter a number:11 11 is odd number

IF( ) … else ….STATEMENT Example // C Program to check whether a person is eligible to vote or not. #include <stdio.h> int main() { int age; printf("Enter your age?"); scanf("%d",&age); if(age>=18) { printf("You are eligible to vote..."); } else { printf("Sorry ... you can't vote"); } } Output1: Enter your age?18 You are eligible to vote... Output2: Enter your age?13 Sorry ... you can't vote

IF( ) … else ….STATEMENT Example // Program to check whether an integer is positive or negative // This program considers 0 as a positive number #include <stdio.h> int main() { int number; printf("Enter an integer: “); scanf(“%d”, &number); if (number >= 0) { printf("You entered a positive integer: %d”, number ); } else { printf(" "You entered a negative integer : %d”, number ); } cout << "This line is always printed."; } Output1: Enter an integer: 4 You entered a positive integer: 4. This line is always printed. Output2: Enter an integer: - 4 You entered a negative integer: -4. This line is always printed.

LOGICAL OPERATORS IN C Note: a and b are both relational expression here

NESTING OF IF…..ELSE STATEMENTS ⚫When a series of decisionsare involved, we may have to use more than one if….else statements, in nested form as follows

Here, if the condition 1 is false then it skipped tostatement 3. But if the condition 1 is true, then it testscondition 2.  If condition 2 is true then it executes statement 1 and if false then it executes statement 2.  Then the control is transferred to the statement x. This can also be shown by the following flowchart, NESTING OF IF…..ELSE STATEMENTS

Program /*Selecting the largestof threevalues*/ main() { float A, B, C; printf(“Enter three values n”); scanf(“|%f %f %f”,&A, &B, &C); printf(“nLargest value is:”); if(A > B) { if(A > C) printf(“%f n”,A); else printf(“%f n”,C); } else { if(C > B) printf(“%f n”,C); else printf(“%f n”,B); } } OUTPUT Enter three values: 5 8 24 Largest value is 24

 This construct is known as the else if ladder. The conditions are evaluated from the top, downwards. This can be shown by the following flowchart The else if ladder

The else if ladder  When a multipathdecision is involved then we use else if ladder.  A multipath decision is a chain of ifs in which the statement associated witheach else is an if.  Ittakes the following general form,

THE SWITCH STATEMENT ⚫Switch statement is used for complex programs when the numberof alternatives increases. ⚫The switch statement tests the value of the given variable against the list of case values and when a match is found, a block of statements associated with thatcase is executed.

SWITCH STATEMENT ⚫ Thegeneral form of switch statement is switch(expression) { casevalue-1: block-1 break; casevalue-2: block-2 break; ……. ……. default: default-block break; } statement-x;

Example: index = marks / 10; switch(index) { case 10: case 9: case 8: grade = “Honours”; break; case 7: case 6: grade = “firstdivision”; break; case 5: grade = “second division”; break; case 4: grade = “third division”; break; default: grade = “first division”; break } printf(“%s n”,grade); ………….

THE ?: OPERATOR ⚫ The C language has an unusual operator, useful for making two- waydecisions. ⚫ This operator is a combination of ? and : and takes three operands. ⚫ It isof the form exp1?exp2:exp 3 ⚫ Here exp1 is evaluated first. If it is true then the expression exp2 is evaluated and becomes thevalue of theexpression. ⚫ If exp1 is false then exp3 is evaluated and its value becomes the valueof theexpression. Eg: if(x < 0) flag = 0; else flag = 1; can be written as flag = (x < 0)? 0 : 1;

UNCONDITIONAL STATEMENTS - THE GOTO STATEMENT C supports the goto statement to branchunconditionally from one point of the program toanother. 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 and must be followed byacolon.

DECISION MAKING AND LOOPING  In looping, a sequence of statements are executed until some conditions for terminationof the loopare satisfied.  In looping, a sequence of statements are executed until some conditions for terminationof the loopare satisfied.  A program loop therefore consists of two segments, one known as the body of the loop and the other known as the control statements.

Cont.. Depending on the position of the control statements in the loop, a control structure may be classified either as an entry-controlled loop or as the exit-controlled loop.

Loops In C ⚫The C language provides for three loop constructs for performing loopoperations. ⚫Theyare: The whilestatement The dostatement The forstatement

THE WHILE STATEMENT ⚫The basic formatof the while statement is while(testcondition) { bodyof the loop } ⚫ The while isan entry–controlled loop statement. ⚫ The test-condition is evaluated and if the condition is true, then the bodyof the loop is executed. ⚫ After execution of the body, the test-condition is once again evaluated and if it is true, the body is executed onceagain. ⚫ This process of repeated execution of the body continues until the test- condition finally becomes false and the control is transferred out of the loop.

Example of WHILE Loop Bodyof the loop test condn? while(testcondition) { bodyof the loop } sum = 0; n = 1; while(n <= 10) { sum = sum + n* n; n = n + 1; } printf(“sum = %d n”,sum);

THE DO STATEMENT ⚫In while loop the body of the loop may not be executed at all if the condition is not satisfied at the very first attempt. ⚫Such situations can be handled with the help of the do statement. do { body of the loop } while(test condition);

Cont.. ⚫Since the test-condition is evaluated at the bottom of the loop, the do…..while construct provides an exit-controlled loop and therefore the body of the loop is always executed at least once. Eg: do { printf(“Inputa numbern”); number= getnum(); } while(number> 0);

Difference between While( ) loop and Do….while() loop

THE FOR STATEMENT ⚫The for loop is another entry-controlled loop that provides a more concise loop control structure ⚫Thegeneral form of the for loop is for(initialization ; test-condition ; increment/Decrement) { body of the loop }

THE FOR STATEMENT for(initialization ; test-condition ; increment/Decrement) { body of the loop }

Cont.. ⚫ The execution of the forstatement isas follows:  Initialization of the control variables is done first.  Thevalue of thecontrol variable is tested using the test-condition.  If the condition is true, the body of the loop is executed; otherwise the loop is terminated and the execution continues with the statementthat immediately follows the loop.  When the body of the loop is executed, the control is transferred back to the for statement after evaluating the last statement in the loop.  Now, the control variable is either incremented or decremented as perthecondition.

Cont.. ⚫Eg 2) sum = 0; for(i = 1; i < 20; ++i) { sum =sum + i; printf(“%d %d n”,sum); } for(initialization ; test-condition ; increment/Devrement) { bodyof the loop }

For Statement ⚫Eg 1) for(x = 0; x <= 9; x = x + 1) { printf)”%d” ,x); } printf(“n”); ⚫ The multiplearguments in the incrementsectionare possible and separated by commas.

Nesting of For Loops ⚫C allowsone forstatementwithin anotherfor statement.

Cont.. ⚫ Eg: ⚫ ⚫ ⚫ for(row = 1; row <= ROWMAX; ++row) ⚫ { ⚫ for(column = 1; column < = COLMAX; ++column) ⚫ { ⚫ y = row * column; ⚫ printf(“%4d” , y); ⚫ } ⚫ printf(“n”); ⚫ } ⚫

JUMPS IN LOOPS  C permits a jump from one statement to another within a loop as well as the jumpoutof a loop. Jumping outof a Loop  An early exit from a loop can be accomplished by using the break statementor thegoto statement.  When the break statement is encountered inside a loop, the loop is immediately exited and the program continues with thestatement immediately following the loop.  When the loops are nested, the break would only exit from the loop containing it. That is, the break will exit only a single loop.

Skipping a part of a Loop ⚫Like the break statement, C supports another similar statementcalled thecontinue statement. ⚫However, unlike the break which causes the loop to be terminated, the continue, as the name implies, causes the loop to be continued with the next iteration after skipping any statements in between. ⚫The continue statement tells the compiler, FOLLOWING STATEMENTS AND CONTINUE WITH ITERATION”. ⚫The formatof thecontinue statement is simply “SKIP THE THE NEXT continue;

Bypassing and continuing I Loops

References 1. http://www.computer-books.us/c_0008.php 2. http://www.computer-books.us/c_0009 3. http://www.computer-books.us/c_2.php 4. www.tutorialspoint.com/cprogramming/cprogramming_pdf. 5. Programming in C by yashwant kanitkar 6. ANSI C by E.balagurusamy- TMG publication 7. Computer programming and Utilization by sanjay shah Mahajan Publication 8. www.cprogramming.com/books.html

Basics of Control Statement in C Languages

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