Mastering Conditional Statements: If, Else, and Switch in Programming

1. Chapter 5 • See chapter 4 notes for the following topics: • Relational operators • Logical operators & expressions The if statement …conditional statement for control transfer The switch statement …multiple-conditional statement for control transfer Professor Jodi Neely-Ritz CGS3460

2. The simple if statement • Allows a program to pick one of two alternatives… • The simplest form of the if statement has the syntax if (conditions) statement; • Examples : if ( a > 0 ) a = a + 1; if ( b ! = 2 ) b--; if ( ( a == 1) || (b == 0 ) ) i = i + 2; Professor Jodi Neely-Ritz CGS3460

3. Compound Statements • To execute multiple statements (block of statements) • Syntax : if (conditions) { statement 1; statement 2; … … … … … … statement n; } Professor Jodi Neely-Ritz CGS3460

4. Compound Statements – an example i = 5; if ( ( a > b ) && ( a ! = 0 ) ) { a = a + 1; printf(“The value of ‘a’ has been incremented… \n”); b = b – 1; printf(“The value of ‘b’ has been decremented… \n”); i = i + 1; k = k + 3; } printf(“The value of i is %d\n”,i); a = 5, b = 3  i = ?? a = 0, b = -2  i = ?? a = 2, b = 7  i = ?? Professor Jodi Neely-Ritz CGS3460

5. The else clause • This clause is used to provide an alternate segment of code • Syntax of the if… else…statement if (conditions) { statement 1; statement 2; } else { statement 3; statement 4; } Professor Jodi Neely-Ritz CGS3460

6. The else clause – an example if ((a >= b) && (b >= c)) { printf(“the value of a = %d\n”,a); printf(“executed if clause\n”); i = i + 1; } else { printf(“executed else clause”); k = k - 4; } Professor Jodi Neely-Ritz CGS3460

7. Nested If statements Any level of nesting is allowed with the if… else… statement if (conditions 1) { if (conditions 2) statement 2; else statement 3; } else { if (conditions 3) { statement 3; statement 4; } } Professor Jodi Neely-Ritz CGS3460

8. Cascaded If statements • Provision to check multiple conditions, providing alternatives for each of the cases… if (conditions 1) { segment 1 } else if (conditions 2) { segment 2 } else if (conditions 3) { segment 3 } … … else { default segment } Professor Jodi Neely-Ritz CGS3460

9. Dangling else… if (conditions 1) if (conditions 2) statement 1; else statement 2; • Here, the else corresponds to the second if statement though it appears to correspond to the first if statement • The compiler uses such a dangling (ambiguous) else to correspond to the last unbalanced if statement if (conditions 1) { if (conditions 2) statement 1; } else statement 2; /*remedied program*/ Professor Jodi Neely-Ritz CGS3460

10. Conditional operators if ( a > b) i = i + 1; else i = i – 1; The above segment can be written in this format : ( a > b ) ? i = i + 1 : i = i – 1 (or) i = (a > b) ? i + 1 : i – 1 Professor Jodi Neely-Ritz CGS3460

11. Boolean values • TRUE and FALSE are defined by most compilers as 1 and 0 • While checking a condition, the if statement checks to see if the condition is “logically true” int lock; … … if ( lock == TRUE ) statement 1; else statement 2; Professor Jodi Neely-Ritz CGS3460

12. The switch statement • This statement is used where there may be multiple input values for a single condition and different output segments correspond to each individual case int i; … … switch ( i ) { case 1 : statement 1; break; case 2 : statement 2; break; … … … … … … … … … … … … … … … … … … … … default : statement; break; } Professor Jodi Neely-Ritz CGS3460

13. The switch statement – an example int month; … … switch ( month ) { case 1 : printf(“Jan\n”); break; case 2 : printf(“Feb\n”); break; … … … … … … … … … … … … … … … … … … … … case 12 : printf(“Dec\n”); break; default : printf(“Error : Invalid month no.\n”); } Professor Jodi Neely-Ritz CGS3460

14. The break clause in the switch statement • The break clause in used in the switch statement to exit the normal control of that segment and exit the entire switch construct • It returns control to the next line after the switch statement • Each case keyword is merely a label to which control jumps • Condition checking is done when the compiler sees the switch statement and control is passed to the corresponding case • Without the break clause, control will ‘fall through into’ other sections that follow that required section Professor Jodi Neely-Ritz CGS3460