1. CSCI 171 Presentation 3

2. Operators Instructs C to perform some operation Assignment = Mathematical Relational Logical

3. Relational Operators Used to compare expressions Equal= = Greater than> Greater than or equal to>= Less than< Less than or equal to<= Not equal!=

4. Tip Do not confuse = (assignment) with = = (logical comparison of equality) Common errors: x = = z + 2; if (x = 3)...

5. if statement General format 1: if (expression) statement; General format 2: if (expression) { statement 1; statement 2; …. Statement n; }

6. Example if scanf(“%f”, &salary) if (salary > 0) { net = salary - (salary * tax); printf(“The net salary is %f”, net); }

7. Sample if with else scanf(“%f”, &salary) if (salary > 0) { net = salary - (salary * tax); printf(“The net salary is %f”, net); } else printf(“Incorrect input”);

8. Sample Program 3.1 #include int main( void ) { int y = 0; printf("Please enter a value for y: "); scanf("%d", &y); if (y >= 1000) printf("\nYou have entered a large number."); printf("\nIt is at greater than or equal to 1000."); return 0; }

9. The conditional operator compared to the if statement z = (x < y) ? x : y; Is equivalent to: if (x < y) z = x; else z = y;

10. Sample Program 3.2 #include int main( void ) { int y = 0; printf("Please enter a value for y: "); scanf("%d", &y); !(y%4)? printf(“y is divisible by 4") : printf(“y is not divisible by 4"); }

11. Relational Expressions Relational expressions evaluate to: 0 (false) 1 (true) Ex: x = (5 = = 5) x holds the value 1

12. Example x = (12 < 62); printf(“%d”, x); x = (5 != 3); printf(“ %d”, x); x = (12 < 62) + (5 != 3) + (5 < 3); printf(“ %d”, x); Output is as follows: 1 1 2

13. Precedence of Relational Operators Relational operators have lower precedence than mathematical operators if ((x + 2) > y) is the same as if (x + 2 > y)

14. Tip Whenever possible, avoid the not operator Ex: if (x != 5) statement1; else statement2; Is equivalent to: if (x == 5) statement2; else statement1;

15. Logical Operators AND&&if (exp1 && exp2) –True if both exp1 and exp2 are true OR||if (exp1 || exp2) –True if either exp1 or exp2 is true NOT!if (!exp1) –True if exp1 is false Precedence –NOT, AND, OR

16. Logical Operator Examples (3 != 5) || (6 < 8)true (3 != 5) || (6 > 8) && (9 = = 3)true ((3 != 5) || (6 > 8)) && (9 = = 3)false ((3 != 5) || (6 > 8)) && !(9 = = 3)true 3true 0false !3false

17. Sample Program 3.3 #include //1. Figure the output for input of a = 3, b = 5, c = 3 //2. Is there anyway for both blocks 3 and 4 to be entered? //3. Rewrite the first if statement using DeMorgan's law int main( void ) { int a = 0, b = 0, c = 0; printf("Enter a, b, and c (separated by commas): "); scanf("%d, %d, %d", &a, &b, &c); if (!((a 3))) printf("\nBlock 1 entered"); else printf("\nBlock 2 entered"); if ((a 3) && (c == 2)) printf("\nBlock 3 entered"); if (((a 3)) && (c == 2)) printf("\nBlock 4 entered"); }

18. The switch statement Program control based on an expression with more than 2 possible values Similar functionality to if statement

19. General form for a switch General form of switch statement: switch(expression) { case template1: statements; case template2: statements; … case templaten: statements; default: statements; }

20. Concrete example of switch switch(i) { case 1: printf(”The number is 1”); case 2: printf(“The number is 2”); case 3: printf(”The number is 3”); default: printf(”The number is not 1, 2, or 3"); }

21. Evaluation of a switch statement If expression matches a template, control passes to first statement within that template If no match, control passes to first statement within default If no match and no default, control passed to first statement after switch structure

22. Output of switch statement switch(i) { case 1: printf(”The number is 1\n”); case 2: printf(“The number is 2\n”); case 3: printf(”The number is 3\n”); default: printf(”The number is not 1, 2, or 3\n"); } If i = 1 Output: The number is 1 The number is 2 The number is 3 The number is not 1, 2, or 3

23. Correct way to code a switch switch(i) { case 1: printf(”The number is 1\n”); break; case 2: printf(“The number is 2\n”); break; case 3: printf(”The number is 3\n”); break; default: printf(”The number is not 1, 2, or 3\n"); }

24. Sample Program 3.4 //Run the following program and fix any errors //Once the program compiles cleanly and runs correctly, //change it to allow for all 4 arithmetic operations #include int main( void ) { char operator = 0; int a = 0, b = 0; printf("Enter the first integer: "); scanf("%lf", &a); printf("Enter the second integer: "); scanf("%lf", b); print("Enter the calculation you would like (+ or -): ") scanf(" %c", &operator); switch(operator) { case '+': printf("\na + b is: %d", a + b); case '-': printf("\na - b is: %d", a - b); default: printf("\nSorry, you did not enter a valid operator."); }