Using For Loops
For Loops
For loops are considered pre-test loops.
A for loop header consists of three parts:
- An intialization expression declares and initializes a variable that is used to track the number of times the loop iterates. Happens once at the start of the loop.
- The Boolean expression controls whether the loop body is executed or not. If it evaluates to
true the body is executed. If the boolean expression evaluates to false, the body is not executed and the loop stops.
- The step expression is sometimes referred to as the increment expression. This expression changes the variable in the variable in the initialization expression and typically works toward making the Boolean expression
false.
NOTE There are cases when parts of the header are left blank.
The general format of a for loop is as follows:
for (<initialization expression>; <Boolean expression>; <step expression>) {
//statments
}
Tracing For Loops
Your Turn
Let's try it in the Java Playground.
- Trace the code and predict the output of the code.
- Run the code to determine if your prediction is correct.
- Modify
value to be assigned 100. Predict the output of the code. Run the code to determine if your prediction is correct.
- Modify
value to be assigned 101. Predict the output of the code. Run the code to detemrine if your prediction is correct.
- Modify
value to be assigned 1 and value++ to be value -= 2. Predict the output of the code. Run the code to determine if your prediciton is correct.
Printing Odd Numbers
- Trace the code and predict the output of the code.
- Run the code to determine if your prediction is correct.
- Modify
value to be assigned 9. Predict the output of the code. Run the code to determine if your prediction is correct.
- Modify
value to be assigned 10. Predict the output of the code. Run the code to detemrine if your prediction is correct.
- Modify
value to be assigned 1 and value += 2 to be value -= 2. Predict the output of the code. Run the code to determine if your prediciton is correct.
Computing Your Average
This program prompts the user to enter the number of grades. Once all the grades are entered, it computes the average. It's important to initialize numGrades to 0 before any grades are entered. This variable needs an initial value in order to be a part of a sum.
int totalGrades = 0;
String input = IO.readln("How many grades?");
int numGrades = Integer.parseInt(input);
int grade = 0;
for (int gradeCount = 1; gradeCount <= numGrades; gradeCount++) {
String input = IO.readln("Enter a grade.");
grade = Integer.parseInt(input);
totalGrades += grade;
}
if (numGrades != 0) {
IO.print(totalGrades/numGrades);
}
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