The article directories

  • Multiple cycle control
    • 1. Introduction
    • 2. Analysis of multiple cycle execution steps:
    • 3. Application Examples:
    • 4. Classic print pyramid

Multiple cycle control

1. Introduction

  1. Nested loops are formed by placing one loop inside another. Where, for,while,do… While can be either an outer loop or an inner loop. [Generally, it is recommended to use two layers, no more than three layers, otherwise, the code is not readable.]
  2. Essentially, a nested loop is a loop body that treats the inner loop as the outer loop. If the loop condition of the inner loop is false, the inner loop can be completely broken, and the outer loop can be finished and the next loop can be started.
  3. Let the number of outer loops bemThe inner layer isnThe inner loop body actually needs to executem*n 次

2. Analysis of multiple cycle execution steps:

  • Please analyze the following multiple loop execution steps and write the output => memory analysis

	for(int i = 0; i < 2; i++) { 
		for( int j = 0; j < 3; j++) {
		    System.out.println("i=" + i + "j="+ j); }}Copy the code

3. Application Examples:

MulForExercise01.java

(1) Count the scores of 3 classes, each class has 5 students, calculate the average score of each class and the average score of all classes [students’ scores are input from the keyboard].

  • Analysis of ideas:
  1. Change numerous for brief

    (1) First calculate the scores of 5 students in a class and score evenlyfor

    1.1 createScannerObject then receives user input

    1.2 To get the average score of the class, define onedoubel sumAccumulate the grades of the five students in the class
	Scanner sc = new Scanner(System.in);
	double sum = 0; // The total score of a class
	for (int j = 1; j <=5; j++){ System.out.println("Please enter the first class number." + j + "A student's grade:");
	    double score = sc.nextDouble();
	    sum += score; / / cumulative
	    System.out.println("The results are:"+score);
	}
	// Because sum is the total score of 5 students
	System.out.println("sum="+sum+"Average score ="+(sum /5 ));
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(2) Count the average score of 3 classes (5 students in each class), add a for loop I to the outer layer, because each class needs to calculate the total score and average score of the students in each class, so nest a layer of for loop 3 in the outer layer, and finally change the input class to the I class

	Scanner sc = new Scanner(System.in);
	for (int i = 1; i <=3; i++) {// I stands for class
	    double sum = 0; // The total score of a class
	    for (int j = 1; j <= 5; j++) {  //j stands for student
	        System.out.println("Please enter no"+i+"First in class." + j + "A student's grade:");
	        double score = sc.nextDouble();
	        sum += score; / / cumulative
	        System.out.println("The results are:" + score);
	    }
	    // Because sum is the total score of 5 students
	    System.out.println("sum=" + sum + "Average score =" + (sum / 5));
	}
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(3) Average scores of all classes

3.1 Define a variable, 'double totalScore' to accumulate the scores of all students 3.2 When the multiple loop is over, 'totalScore/(3 * 5)'Copy the code
	Scanner sc = new Scanner(System.in);
	double totalScore = 0;// Accumulate the total scores of all students
	for (int i = 1; i <=3; i++) {// I stands for class
	    double sum = 0; // The total score of a class
	    for (int j = 1; j <= 5; j++) {  //j stands for student
	        System.out.println("Please enter no"+i+"First in class." + j + "A student's grade:");
	        double score = sc.nextDouble();
	        sum += score; / / cumulative
	        System.out.println("The results are:" + score);
	    }
	    // Because sum is the total score of 5 students
	    System.out.println("sum=" + sum + "Average score =" + (sum / 5));
	    // Add sum to totalScore
	    totalScore += sum;
	}
	System.out.println("Total score of three classes"+totalScore+"Average score ="+totalScore / 15);
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(4) Count the number of passing students in the three classes

4.1 Defining the variable int passNum = 0; If there is a student whose grade >=60, passNum++ 4.2 if >=60 passNum++Copy the code
	Scanner sc = new Scanner(System.in);
	 double totalScore = 0;// Accumulate the total scores of all students
	 int passNum = 0; // Cumulative number of passes
	 for (int i = 1; i <=3; i++) {// I stands for class
	     double sum = 0; // The total score of a class
	     for (int j = 1; j <= 5; j++) {  //j stands for student
	         System.out.println("Please enter no"+i+"First in class." + j + "A student's grade:");
	         double score = sc.nextDouble();
	         if (score >= 60){
	             passNum++;
	         }
	         sum += score; / / cumulative
	         System.out.println("The results are:" + score);
	     }
	     // Because sum is the total score of 5 students
	     System.out.println("sum=" + sum + "Average score =" + (sum / 5));
	     // Add sum to totalScore
	     totalScore += sum;
	 }
	 System.out.println("Total score of three classes"+totalScore+"Average score ="+totalScore / 15);
	 System.out.println("Number of passes ="+passNum);
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(5) [efficiency, readability, structure] can be optimized, and the number of class and students can be replaced by variables respectively

	Scanner sc = new Scanner(System.in);
    double totalScore = 0;// Accumulate the total scores of all students
    int passNum = 0; // Cumulative number of passes
    int classNum = 3; // Number of classes
    int stuNum = 5; // Number of students
    for (int i = 1; i <= classNum; i++) {// I stands for class
        double sum = 0; // The total score of a class
        for (int j = 1; j <= stuNum; j++) {  //j stands for student
            System.out.println("Please enter no"+i+"First in class." + j + "A student's grade:");
            double score = sc.nextDouble();
            if (score >= 60){
                passNum++;
            }
            sum += score; / / cumulative
            System.out.println("The results are:" + score);
        }
        // Because sum is the total score of 5 students
        System.out.println("sum=" + sum + "Average score =" + (sum / stuNum));
        // Add sum to totalScore
        totalScore += sum;
    }
    System.out.println("Total score of three classes"+totalScore+"Average score ="+totalScore / classNum*stuNum);
    System.out.println("Number of passes ="+passNum);
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(2) Count the number of passing students in three classes, each class has 5 students.

(3) Print out the multiplication table

	for	(int i = 1; i <= 9; i++){
		  for(int j = 1; j <= i; j++){
		  // "\t" this is the default TAB symbol of the JAVA language. Using this symbol, the printed multiplication table is nice
		      System.out.print("" + i + "*" + j + "=" + (i * j)+"\t");
		      if(i == j){
		          System.out.print("\n");// When the newline condition is true, the newline is printed}}Copy the code

4. Classic print pyramid

  • Use the for loop to complete the following example

    Please write a program that can receive an integer, representing the totalLevel, and print out the pyramid. (Stars.java) [Make it simple. Die before you live]

  • 1. Print a rectangle first
	*****
	*****
	*****
	*****
	*****
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  for (int i = 1; i <= 5; i++) {
            System.out.println("* * * * *");
        }
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  1. Print half a pyramid
	*    	// Level 1 has 1 *支那// Layer 2 has 2 ** * *// There are 3 * * at layer 3* * * *// There are 4 * * at layer 4* * * * *// There are 5 * * at level 5
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	for (int i = 1; i <= 5; i++) {  // I indicates the number of layers
		  // Control the number of * in each layer
		  for (int j = 1; j <= i; j++) {
		      System.out.print("*");
		  }
		  // After each layer is printed, the line is wrapped
		  System.out.println("");
		}
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  1. Print the whole pyramid
						     2- * layer1
	*       // Layer 1 has 1 * 2 * 1 -1 has 4=(total number of layers -1) Spaces* * *// Layer 2 has 3 * 2 * 2-1 3=(total number of layers -2) Spaces* * * * *// Layer 3 has 5 * 2 * 3 -1 has 2=(total layer -3) Spaces* * * * * * *// Layer 4 has 7 * 2 * 4 -1 has 1=(total number of layers -4) Spaces* * * * * * * * *// Layer 5 has 9 * 2 * 5 -1 has 0=(total number of layers -5) Spaces
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	for (int i = 1; i <= 5; i++) {  // I indicates the number of layers

	    // Before output *, output corresponding space = total number of layers - current layer
	    for (int k = 1; k <= 5-i; k++){
	        System.out.print("");
	    }
	    
	    // Control the number of * in each layer
	    for (int j = 1; j <= 2 * i - 1; j++) {
	        System.out.print("*");
	    }
	    
	    // After each layer is printed, the line is wrapped
	    System.out.println("");
	}
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  1. Print hollow pyramids [hardest]
	*       // The first position of the current row is *, and the last position is *
   * *      // The first position of the current row is *, and the last position is *
  *   *     // Level 3 has 2 * * the first position of the current row is *, and the last position is *
 *     *    // Level 4 has 2 * * the first position of the current row is *, and the last position is ** * * * * * * * *// Layer 5 has 9 * all outputs *
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	for (int i = 1; i <= 5; i++) {  // I indicates the number of layers

	    // Before output *, output corresponding space = total number of layers - current layer
	    for (int k = 1; k <= 5-i; k++){
	        System.out.print("");
	    }
	
	    // Control the number of * in each layer
	    for (int j = 1; j <= 2 * i - 1; j++) {
	        // The first position of the current line is *, the last position is also *, the last layer all output *
	        if (j == 1 || j == 2 * i - 1 || i == 5){
	            System.out.print("*");
	        }else { // Output Spaces in other cases
	            System.out.print(""); }}// After each layer is printed, the line is wrapped
	    System.out.println("");
	}
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  1. Die before you live: 5 layers of variablesint totalLevel = 5;
  • Change the 5 to 10
		int totalLeavel = 10;
	    for (int i = 1; i <= totalLeavel; i++) {  // I indicates the number of layers
	
	        // Before output *, output corresponding space = total number of layers - current layer
	        for (int k = 1; k <= totalLeavel-i; k++){
	            System.out.print("");
	        }
	
	        // Control the number of * in each layer
	        for (int j = 1; j <= 2 * i - 1; j++) {
	            // The first position of the current line is *, the last position is also *, the last layer all output *
	            if (j == 1 || j == 2 * i - 1 || i == totalLeavel){
	                System.out.print("*");
	            }else { // Output Spaces in other cases
	                System.out.print(""); }}// After each layer is printed, the line is wrapped
	        System.out.println(""); }}Copy the code