1. Relational, Logical, and Equality Operators
Think of these as returning true/false (logical) values, represented by integer values 0 (false) and 1 (true)
Relational operators: >, <=, <, <=
Equalify operators: ==, !=
These binary operators can be applied to built-in data types such as int, float, etc. (will discuss strings in future)
Examples: (3 != 4) evaluates to 0. Hence, printf( “%d”, (3 != 4)); (in a program) would print out 0.
IMPORTANT! == (two equals) vs. = (one equal) common source of programmer errors in C.
Logical operators: &&, ||, !

2. Example: Logical Operators
#include <stdio.h>
void main() {
int i, j;
for( i = 0; i < 2; i++ )
for( j = 0; j < 2; j++ )
printf( “%d AND %d = %d, %d OR %d = %d\n”,
i, j, i && j, i, j, i || j ); }

3. If-else Syntax: if( expression ) statement1 [else statement2]
Recall that statements are either single commands terminated by semicolons, or blocks of commands delimited by braces {}.
if( expression ) same as if( expression != 0 )
Q: What’s better, if( expression ) … else …
Or if( !expression) … else …
if(( year % 4 == 0 && year % 100 != 0 ) ||
year % 400 == 0 )
printf( “%d is a leap year\n”, year );

4. If-else-if-else… Syntax: if( expression ) statement1
else if( expression2 )
statement2
else if( expression3 )
statement3 …
else
statement
Temptation: Continually indent.
What’s the equivalent series of if statements (no elses)?
Beware “dangling else problem” – if if else

5. Example: If-else #include <stdio.h> void main() {
int low, high, i;
scanf( “%d”, &low );
scanf( “%d”, &high );
for( i = low; i <= high; i++ )
if( i % 3 == 0 )
printf( “%d is divisible by 3\n”,
i );
else if( i % 2 == 0 )
printf( “%d is divisible by 2, but not 3\n”, i ); }

6. Switch & Case / for, while
Syntax:
switch( int-valued-exp ) {
case const-expr:
statements
[break;] …
default: }
For( exp1; exp2; exp3 ) {
statement(s) }
Equivalent to:
exp1;
While( exp2 )
exp3
Can include break;
How to go other way? do {
statement(s)
} while( exp );

7. Switch example switch( month ) {
case 1: case 3: case 5: case 7: case 8:
case 10:
case 12:
printf( “31 days.\n” );
break;
case 2:
printf( “28 days.\n” );
default;
printf( “30 days.\n” ); }

8. Finding maximum values
#include <stdio.h>
void main() {
int num, max = -1, i, user_input;
printf( “How many positive ints you gonna enter?” );
scanf( “%d”, &num );
for( i = 0; i < num; i++ )
scanf( “%d”, &user_input );
if( user_input > max )
max = user_input; }
printf( “Your maximum value was: %d\n”, max );