Control Statements in C . 1.Decision making statements 2.Looping statements 3.Branching statements .
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Transcript of Control Statements in C . 1.Decision making statements 2.Looping statements 3.Branching statements .
Control Statements in C
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1.Decision making statements
2.Looping statements
3.Branching statements
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Decision making statements
• Used to making decisions based upon certain condition
• Conditions are decide whether or not a statement should be executed
• Keywords if and else for condition statement.
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Decision making statements
• If
• If else
• Else if
• Nested if
• switch
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If,else if,else Selection Structures
• Selection structures permit alternate actions based on the evaluation of logical expressions.
• The logical expressions evaluate as either true or false, and the action takes place if and only if the expression is true.
• When the expression is false, the program may take alternate action(s), or it may evaluate another expression to determine what to do next.
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If,else if ,else structures
• A simple if structure is called a single-selection structure because it either selects or ignores a single action.
• The if / else structure is called a double-selection structure because it selects between two different actions.
• Nested if / else structures test for multiple cases by placing if / else structures inside other if / else structures.
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If,if else Syntax
• Syntax for the if selection structure is as follows:
if ( this logical expression is true ) statement ;
• Syntax for the if / else selection structure is as follows:
if ( this logical expression is true ) statement ;
else statement ;
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Example
• A very simple program:
#include <stdio.h>
int main ( )
{
int a = 1, b = 2, c ;
if (a > b) c = a;
else c = b;
}
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If,if else structures• The if selection structure is often written as:
if ( this logical expression is true )
statement ;
• And, the if / else selection structure is often written as:
if ( this logical expression is true )statement ;
else statement ;
no semi-colon!
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Example
• Often, the earlier example is written this way:
#include <stdio.h>int main ( ){ int a = 1, b = 2, c ; if (a > b)
c = a ; else
c = b ;}
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If ,else if, else structures
• Syntax for the if / else if / else selection structure is as follows:
if ( this logical expression is true )
statement ;
else if ( this logical expression is true )
statement ;
else
statement ;
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else if syntax
• The actual syntax for the multiple if / else if / else selection structure is as follows:
if ( this logical expression is true ) statement ;
else if ( this logical expression is true )statement ;
else if ( this logical expression is true )statement ;
else statement ;
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Simple Program Using if / else if / else
#include <stdio.h>int main ( ){ int a , b ; printf ("Enter values for a and b > ") ; scanf ("%d%d", &a, &b ) ; if ( a < b ) printf ("a is less than\n") ; else if ( a == b ) printf (" a is equal to b\n") ; else printf ("a is larger than b\n") ;}
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Grading program using if,else if , else
/* This program associates letter grades with numeric test scores */
#include <stdio.h>
int main ( ){
int score ;printf ("enter your test score >") ;scanf ("%d", &score) ;
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if (score >= 90)
printf ("Your score of %d is a A\n", score) ;
else if (score >= 80 && score < 90)
printf ("Your score of %d is a B\n", score) ;
else if (score >= 70)
printf ("Your score of %d is a C\n", score) ;
else if (score >= 60)
printf ("Your score of %d is a D\n", score) ;
else
printf ("Your score of %d is an E\n", score) ;
}
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Nested if statement The if statement may itself contain another if statement is
known as nested if statement.
Syntax:
if (condition1) if (condition2) statement-1; else statement-2; else statement-3;
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The switch Multiple-Selection Structure
switch◦ Useful when a variable or expression is tested for all the values it can
assume and different actions are taken.
Format◦ Series of case labels and an optional default caseswitch ( value ){case '1':
actions
case '2':actions
default:actions
}
◦ break; causes exit from structure
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The switch Multiple-Selection Structure
true
false
.
.
.
case a case a action(s) break
case b case b action(s) break
false
false
case z case z action(s) break
true
true
default action(s)
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1. Initialize variables
2. Input data
2.1 Use switch loop to update count
1 /* Fig. 4.7: fig04_07.c2 Counting letter grades */3 #include <stdio.h>45 int main()6 {7 int grade;8 int aCount = 0, bCount = 0, cCount = 0, 9 dCount = 0, fCount = 0;1011 printf( "Enter the letter grades.\n" );12 printf( "Enter the EOF character to end input.\n" );1314 while ( ( grade = getchar() ) != EOF ) {1516 switch ( grade ) { /* switch nested in while */1718 case 'A': case 'a': /* grade was uppercase A */19 ++aCount; /* or lowercase a */20 break;2122 case 'B': case 'b': /* grade was uppercase B */23 ++bCount; /* or lowercase b */24 break;2526 case 'C': case 'c': /* grade was uppercase C */27 ++cCount; /* or lowercase c */28 break;2930 case 'D': case 'd': /* grade was uppercase D */31 ++dCount; /* or lowercase d */32 break;
2.1 Use switch loop to update count
3. Print results
33
34 case 'F': case 'f': /* grade was uppercase F */
35 ++fCount; /* or lowercase f */
36 break;
37
38 case '\n': case' ': /* ignore these in input */
39 break;
40
41 default: /* catch all other characters */
42 printf( "Incorrect letter grade entered." );
43 printf( " Enter a new grade.\n" );
44 break;
45 }
46 }
47
48 printf( "\nTotals for each letter grade are:\n" );
49 printf( "A: %d\n", aCount );
50 printf( "B: %d\n", bCount );
51 printf( "C: %d\n", cCount );
52 printf( "D: %d\n", dCount );
53 printf( "F: %d\n", fCount );
54
55 return 0;
56 }
Program Output
Enter the letter grades.Enter the EOF character to end input.ABCCADFCEIncorrect letter grade entered. Enter a new grade.DAB Totals for each letter grade are: A: 3B: 2C: 3D: 2F: 1
Iterative(looping) Statements
It allow a set of instructions to be executed or performed several times until certain conditions are met.
KINDS OF LOOPING STATEMENTS
1. for loop
2. while loop
3. do-while loop
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The for loop statement
SYNTAX:for (initialization; condition; increment/decrement){
statement_sequence;}
for is a reserve word in turbo Cinitialization is an assignment statement that is used to set the
loop’s counter.condition is a relational boolean expression that determines
when the loop will exit.increment defines how the loop’s counter will change each time
the loop is repeated.statement_sequence may either be a single Turbo C statement or
block of Turbo C statements that make up the loop body.
No semicolon after last expression
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4.6 Examples Using the for Structure
Program to sum the even numbers from 2 to 100
Program Output
Sum is 2550
1 /* Fig. 4.5: fig04_05.c
2 Summation with for */
3 #include <stdio.h>
4
5 int main()
6 {
7 int sum = 0, number;
8
9 for ( number = 2; number <= 100; number += 2 )
10 sum += number;
11
12 printf( "Sum is %d\n", sum );
13
14 return 0;
15 }
While loop statement
SYNTAX:initialization;while (condition){
statement_sequence;increment/decrement
}
while is a reserve word in turbo Cinitialization is an assignment statement that is used to set the
loop’s counter.condition is a relational Boolean expression that determines when
the loop will exit.increment defines how the loop’s counter will change each time
the loop is repeated.Statement _ sequence may either be a single Turbo C statement or
block of Turbo C statements that make up the loop body.
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The do/while loop statement
SYNTAX:initialization;do{
statement_sequence;increment/decrement
} while (condition)
do-while is a reserve word in turbo Cinitialization is an assignment statement that is used to set the loop’s
counter.condition is a relational Boolean expression that determines when the
loop will exit.increment defines how the loop’s counter will change each time the
loop is repeated.statement_sequence may either be a single Turbo C statement or block
of Turbo C statements that make up the loop body.
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The do/while Repetition Structure
true
false
action(s)
condition
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The do/while Repetition Structure
• Example (letting counter = 1)
do {
printf( "%d ", counter );
} while (++counter <= 10);
Prints the integers from 1 to 10
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1. Initialize variable
2. Loop
3. Print
Program Output
1 /* Fig. 4.9: fig04_09.c
2 Using the do/while repetition structure */
3 #include <stdio.h>
4
5 int main()
6 {
7 int counter = 1;
8
9 do {
10 printf( "%d ", counter );
11 } while ( ++counter <= 10 );
12
13 return 0;
14 }
1 2 3 4 5 6 7 8 9 10
Branching statements
1.break statement
2.continue statement
3.goto statement
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The break Statements
• break– Causes immediate exit from a while, for, do/while or switch structure
– Program execution continues with the first statement after the structure
– Common uses of the break statement• Escape early from a loop
• Skip the remainder of a switch structure
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The continue Statements
• continue– Skips the remaining statements in the body of a while, for or do/while structure • Proceeds with the next iteration of the loop
– while and do/while• Loop-continuation test is evaluated immediately after the continue statement is executed
– for structure• Increment expression is executed, then the loop-continuation test is
evaluated
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The goto statement
The goto statement transfers control to a label. The given label must reside in the same function and can appear before only one statement in the same function.
• Syntax
• statement: labeled-statement
• jump-statement
• jump-statement: goto identifier ;
• labeled-statement: identifier : statement
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1. Initialize variable
2. Loop
3. Print
Program Output
1 /* Fig. 4.12: fig04_12.c
2 Using the continue statement in a for structure */
3 #include <stdio.h>
4
5 int main()
6 {
7 int x;
8
9 for ( x = 1; x <= 10; x++ ) {
10
11 if ( x == 5 )
12 continue; /* skip remaining code in loop only
13 if x == 5 */
14
15 printf( "%d ", x );
16 }
17
18 printf( "\nUsed continue to skip printing the value 5\n" );
19 return 0;
20 }
1 2 3 4 6 7 8 9 10Used continue to skip printing the value 5
