“Zero basis to understand the C language introductory course” — (nine) C language two-dimensional array and loop nesting

Is C really hard? If you don’t see this picture, you can easily learn C by breaking it into parts. The first article: (one) from the learning error The second: (2) not be so hard to do a simple C language development you understand the process Third: (3) easily understand the first C language program Article 4 (four) C language the basic data types and variables of article 5 (five) C language variables, constants, and operating Article 6: (10) The basic array is not so simple. (10) The pointer of C language is originally like this. (11) THE C language custom function is really very simple. (12) the original structure is such a thing :(13) socket server prepared

C language novice 100 error solutions

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Nested loops refer to loops that have code within them, such as a for loop that also has a for loop within it.

Suppose two for loops are nested. The condition for the external for loop to jump out is I <5, the initial value of I is 0, and the external for loop will loop five times. The inner for loop has a loop condition of j<5 and an initial value of j 0. So when the outer loop loops once the inner for loop loops five times; The external loop needs to jump out when the conditions are not valid, and the loop will continue to jump out if the loop is not satisfied obviously for 1 time. This creates an external for loop once and an inner loop five times. Let’s use the example to see, the demo code is as follows:

#include<stdio.h>
void main(a)
{
    int i,j; 
    for(i=0; i<5; i++) {for(j=0; j<5; j++) {printf("The value of I for the outer loop is %d and the value of j for the inner loop is %d\n",i,j); 
        }
		printf("\n"); }}Copy the code

The above code defines two variables, one is I and the other is j. I and j are initialized in the for loop, I =0; With j = 0; This code executes only once during the entire loop and will be executed again unless the loop is restarted from the beginning. The external for loop has the same condition as the internal for loop, the loop variable is less than 5, but the loop variable is different, because the loop variable increases during the loop, because the loop is nested, the external loop is executed once, then the internal loop will execute 5 times.

The running results are as follows:



3.2 Understand the combined use of circular nesting and two-dimensional arrays

In the previous section, we learned that loop nesting causes the outer loop to execute once and the inner loop to execute multiple times. With this in mind, we can use loop nesting to get all the values of a two-dimensional array.

Suppose there is a two-dimensional array with 2 rows and 5 elements in each row. The elements in the first row are [0][1],[0][2],[0][3],[0][4],[0][5], and we can obviously find that the first dimension subscript does not change, but the second subscript is incresed one by one. Then you can use loop nesting to get all the values as follows:

#include<stdio.h>
void main(a)
{
    int a[2] [5] = {1.2.3.4.5.6.7.8.9.10};
    int i,j;
    for(i=0; i<2; i++) {for(j=0; j<5; j++) {printf("Array [%d][%d] is %d\n",i,j,a[i][j]); }}}Copy the code

In the code above, the contents of the outer loop are I less than 2 and increment each time, and the j of the inner loop is less than 5 and increment each time, so the outer loop executes once and the inner loop executes five times. When I of the outer loop is 0, the first time of the inner loop is a[0][0] and the second time is a[0][1]. We take the variables I and j as the subscripts of the array A, and then all the two-dimensional array values will be obtained.

The results are as follows: