IF Structure

Authored by: John Even (edited by Lex Jacobson)

Faculty Supervisor: Al Day

Some material derived from lessons authored by Dr. James Hilliard

HTML Documentation by Larry Genalo Jr.

Date Last Updated: 8/7/95

IF Statement

Form: if (logic) statement

logic is a logical expression

statement is any executable C statement

Execution Sequence for the IF Statement

The logical expression is evaluated as True or False.

If the expression is true, statement is executed. Then the next C statement in the program sequence is executed.

If the expression is false, statement is not executed. The next statement in the program sequence is executed.

Example of IF

if (a==b) printf("a is equal to b.\n");

If a is equal to b, the string is output to the screen. If a is not equal to b, execution continues with the next C statement.

Note: == is the relational operator to test for equality.

Logical Expressions and Relational Operators

Logical expression: Asks a question about two or more variables or arithmetic expressions.

Examples:
Is x less than y?
Is pow(a,2) equal to pow(b,2)?
Is pow(x*x+y*y, 0.5) greater than 10?

Logical Expressions:

Logical Operators

Logical   "AND"

Form:              &&

Examples:  x<y&&a>b
     Interpretation: Is x&lty and a&gtb?

             x&lty&&a*a==b*b

     Interpretation: Is x&lty AND 
                       a squared = b squared?

Logical   "OR"

Form:         ||

Example:   a>=b||a*a<=y Interpretation: Is a>=b or a*a>=y

Block IF Structure

Form:
	  if (logical condition){
	      ___________________________
	      ___________________________
              ___________________________
	     } else {
	      ___________________________
	      ___________________________
	     }