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Making Choices in C if/else statement logical operators break and continue statements switch statement the conditional operator
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Making Choices in C if/else statement logical operators break and continue statements switch statement the conditional operator.

Dec 14, 2015

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Page 1: Making Choices in C if/else statement logical operators break and continue statements switch statement the conditional operator.

Making Choices in C

if/else statement

logical operators

break and continue statements

switch statement

the conditional operator

Page 2: Making Choices in C if/else statement logical operators break and continue statements switch statement the conditional operator.

The if Statement

• Formatif ( condition )program statement;

orif ( condition ) {program statements;

}

• Flow

Condition true?

Program statements

Yes

No

Page 3: Making Choices in C if/else statement logical operators break and continue statements switch statement the conditional operator.

Example

• Calculating the absolute value of an integer

number < 0

number = - number;

Yes

No

printf(“type in your number: “);scanf(“%i”, &number);

if ( number < 0 )number = -number;

printf(“\nThe absolute value is %i\n”, number);

Page 4: Making Choices in C if/else statement logical operators break and continue statements switch statement the conditional operator.

The if-else Statement

• Formatif ( condition )

program statement 1;

else

program statement 2;

• Flow

condition true?

program statement 1

Yes

No

program statement 2

Page 5: Making Choices in C if/else statement logical operators break and continue statements switch statement the conditional operator.

The else if Statement

• Formatif ( condition1 )

program statement 1;

else if (condition2)

program statement 2;

• Flow

condition1 true?

program statement 1

Yes

No

condition2 true?

No

program statement 2

Yes

Page 6: Making Choices in C if/else statement logical operators break and continue statements switch statement the conditional operator.

One exampleif (condition1)

program statement 1;

else if (condition2)

program statement 2;

else

program statement 3;

condition1 true?

program statement 1

Yes

No

condition2 true?

No

program statement 3program

statement 2

Yes

Page 7: Making Choices in C if/else statement logical operators break and continue statements switch statement the conditional operator.

Boolean Variables

• Declaration– Boolean variables are represented by integers

• Value– 0 represents false– 1 representing true, mostly

• Any nonzero value represents true in C

Page 8: Making Choices in C if/else statement logical operators break and continue statements switch statement the conditional operator.

Logical Operators

• Why– Make a decision based on multiple conditions

• What are they

Operator Example Description

|| x < 0 || x > width logical OR

&& x >= 0 && x <= width logical AND

! !(x < 0) logical NOT

Page 9: Making Choices in C if/else statement logical operators break and continue statements switch statement the conditional operator.

Logical OR

• Returns false only if both expressions are false

• Example:for (i=5 ; i<=95; i+=5) {

if((i < 35) || (i > 60)) {

printf(“%i”, i);

}

}

A B A || B

True True True

True False True

False True True

False False False

Page 10: Making Choices in C if/else statement logical operators break and continue statements switch statement the conditional operator.

Logical AND

• Returns true only if both expressions are true

• Example:for (i=5 ; i<=95; i+=5) {

if((i > 35) && (i < 60)) {

printf(“%i”, i);

}

}

A B A && B

True True True

True False False

False True False

False False False

Page 11: Making Choices in C if/else statement logical operators break and continue statements switch statement the conditional operator.

Logical NOT

• Inverts the Boolean value of an expression

• Example:

int a = 0;

if (!a) {

printf(“a is not 0\n”);

}

a = 1;

if (a) {

printf(“a is 1\n”);

}

A !A

True False

False True

Page 12: Making Choices in C if/else statement logical operators break and continue statements switch statement the conditional operator.

Conditional Expressions

• Relational expression using ==, !=, >, >=, <, <=– The value of “relational expression” is 1 if the relation is true, and

0 if false. 

• Operators can be combined with logical operators (with decreasing precedence):– ! (NOT)– && (AND)– || (OR)

• Rules:– && and || are evaluated left to right

• Example:c==' ' || c=='\t' || c=='\n'

Page 13: Making Choices in C if/else statement logical operators break and continue statements switch statement the conditional operator.

Example: Giving Final Grade

A(100-90), B(89-80),C(79-70),D(69-60),F(59-0)

if (score >= 90) grade = ‘A ’;else if (score >= 80) grade = ‘B ’;else if (score >= 70) grade = ‘C ’;else if (score >= 60) grade = ‘D ’;else grade = ‘F ’;

Page 14: Making Choices in C if/else statement logical operators break and continue statements switch statement the conditional operator.

Evaluate a simple expression

• Objective:– Evaluate expression and display results with

input in the form:number operator number

• Example– User input: 12 + 3– Program output: 15

Page 15: Making Choices in C if/else statement logical operators break and continue statements switch statement the conditional operator.

Program#include <stdio.h>

int main(void){ float v1, v2; char operator;

printf("Type in your expression: \n"); scanf("%f %c %f", &v1, &operator, &v2);

if ( operator == '+' ) printf("%.2f\n", v1 + v2); else if ( operator == '-' ) printf("%.2f\n", v1 - v2); else if ( operator == '*' ) printf("%.2f\n", v1 * v2); else if ( operator == '/' ) printf("%.2f\n", v1 / v2);

return 0;}

Need to check v2 == 0?

Page 16: Making Choices in C if/else statement logical operators break and continue statements switch statement the conditional operator.

Corrections

• Changeelse if ( operator == '/' )

printf("%.2f\n", v1 / v2);

toelse if ( operator == '/' )

if ( v2 == 0 )

printf(“Division by zero.\n”);

else

printf("%.2f\n", v1 / v2);

Page 17: Making Choices in C if/else statement logical operators break and continue statements switch statement the conditional operator.

Watch Out for This!!!

• The assignment operator “=“ and the equality operator “==“ ARE VERY DIFFERENT, DO NOT CONFUSE THEM!

• This code compiles and runs, but does not do what you may expect:

if (x = 0) {

x = 1;

}

printf(“x = %i\n,x);

Page 18: Making Choices in C if/else statement logical operators break and continue statements switch statement the conditional operator.

How to get out of a loop prematurely?

• Use the break statement– Skips all subsequent statements in the loop – Exits immediately from the current loop– Continues execution after the loop

• Or the continue statement– Skip subsequent statements in the current iteration– Continue execution with the next iteration

Page 19: Making Choices in C if/else statement logical operators break and continue statements switch statement the conditional operator.

Example – summation of valid scores

int count, n = 10, sum = 0, score;

for (count = 0; count < n; count++){

scanf("%d", &score);

if (score < 0 || score > 100)

continue;

sum = sum + score;

}

Page 20: Making Choices in C if/else statement logical operators break and continue statements switch statement the conditional operator.

Example – summation of valid scores

int count, n = 10, sum = 0, score;

for (count = 0; count < n, count++) {

scanf("%d", &score);

if (score < 0 || score > 100) {

printf(“Bad data. Exiting\n”);

break;

}

sum = sum + score;

}

Page 21: Making Choices in C if/else statement logical operators break and continue statements switch statement the conditional operator.

The switch Statement• When to use

– The value of a variable successively compared against different values

• Formatswitch( expression ) {

case value 1: program statement 1; break;

case value 2: program statement 2; break; ׃׃

case value n: program statement n; break;

default : program statement n+1; break;

}

== value 1

evaluate expression

statement 1Y

N

== value 2

== value n

N

Nstatement n+1

Ystatement 2

Ystatement n

Page 22: Making Choices in C if/else statement logical operators break and continue statements switch statement the conditional operator.

Example switch ( operator ) { case '+': printf("%.2f\n", v1 + v2); break; case '-': printf("%.2f\n", v1 - v2); break; case '*': printf("%.2f\n", v1 * v2); break; case '/': if ( v2 == 0 ) printf(“Division by zero.\n”); else printf("%.2f\n", v1 / v2); break; default: printf("Unknown operator!\n"); break; }

Page 23: Making Choices in C if/else statement logical operators break and continue statements switch statement the conditional operator.

Another exampleswitch (month) { case 1: printf("January"); break; case 2: printf("February"); break; case 3: printf("March"); break; case 4: printf("April"); break; case 5: printf("May"); break; case 6: printf("June"); break; case 7: printf("July"); break; case 8: printf("August"); break; case 9: printf("September"); break; case 10: printf("October"); break; case 11: printf("November"); break; case 12: printf("December"); break; default: printf("Invalid month."); break; }

Page 24: Making Choices in C if/else statement logical operators break and continue statements switch statement the conditional operator.

More on switch Statement

case value 1:

statement 1;

case value 2: statement 2;

break;

== value 1 statement 1Y

N

== value 2

N

Ystatement 2

Usually, this is a BUG! And one that is often very hard to find! “MISSING BREAK”

Page 25: Making Choices in C if/else statement logical operators break and continue statements switch statement the conditional operator.

The conditional operator

• Format:condition ? expression1 : expression2

• Same asif ( condition ) {

expression1;

} else {

expression2;

}

Except: the “?” can be used in an expression.


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