# C language two-dimensional array - learning thirteen

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## Two dimensional array

• General form:
• Type specifier array name [constant expression] [constant expression];
• for example
• int a; Describes an array with three rows and four columns. The array name is a and the type of its subscript variable is integer.
• Storage of two-dimensional array in memory
• Two dimensional array is two-dimensional in concept, but the actual hardware memory is continuously addressed, that is, the memory units are arranged in one-dimensional linear array.
• In C language, a two-dimensional array is arranged in rows, that is, after one row is placed, it is placed in the second row in sequence.

### Reference of two-dimensional array

• General form:
• Array name [subscript] [subscript]
• for example
• b=a/2;
• Subscripts can be integer expressions.
• For example: a, a[2-1][2*2-1]
• The subscript value should be within the defined array size.
• For example: int a; a=3; Wrong definition a is an array of 3 rows and 4 columns. The subscript starts from 0. The maximum subscript of the row is 2 and the maximum subscript of the column is 3

### Initialization of two-dimensional array

• For example: int a   = {1,2,3,4}, {5,6,7,8}, {9,10,11,12};
• Write all data in a flower bracket and assign initial values to each element in the order of array arrangement.
• For example: int a   = {1,2,3,4,5,6,7,8,9,10,11,12};
• For example: int a   = {1}, {2}, {3}; Assign a value to the first column element of each row, and the unassigned element takes the value of 0.
• After assignment
• 1 0 0
• 2 0 0
• 3 0 0
• If all elements are given initial values, the length of the first dimension may not be specified when defining the array, but the length of the second dimension cannot be omitted.
• For example: int a   = {1,2,3,4,5,6,7,8,9,10,11,12};
• It can be written as: int a[]={{1,2,3,4,5,6,7,8,9,10,11,12};

#### example

There is a 3 × 4 matrix, which requires programming to find the value of the element with the largest value, as well as its row number and column number.

```#include<stdio.h>

main()
{
int max, a,i,j,x,y;
max = a;
for (i = 0; i <= 2; i++){
for (j = 0; j <= 3; j++) {
scanf_s("%d", &a[i][j]);
}
}
for (i = 0; i <= 2; i++) {
for (j = 0; j <= 3; j++) {
if (max < a[i][j]) {
max = a[i][j];
x = i+1;
y = j+1;
}
}
}
printf("max=%d,In the first%d OK, page%d column", max, x, y);

}``` Exchange the elements of rows and columns of a two-dimensional array and store them in another two-dimensional array. ```#include<stdio.h>

main()
{
int a,b,i,j;

for (i = 0; i <= 1; i++){
for (j = 0; j <= 3; j++) {
scanf_s("%d", &a[i][j]);

}
}
printf("\n");

for (i = 0; i <= 1; i++) {
for (j = 0; j <= 3; j++) {
b[j][i] = a[i][j];
printf("%d ", a[i][j]);
}
printf("\n");
}
printf("\n");

for (i = 0; i <= 3; i++) {
for (j = 0; j <= 1; j++) {
printf("%d ", b[i][j]);
}
printf("\n");
}
}``` The diagonal of the two-dimensional array a10 is 1 and the others are 0.

```#include<stdio.h>

void main()
{
int a,i,j;

for (i = 0; i <= 9; i++){
for (j = 0; j <= 9; j++) {
if (i == j||i+j==9) {
a[i][j] = 1;
}
else
{
a[i][j] = 0;
}
}
}
printf("\n");

for (i = 0; i <= 9; i++) {
for (j = 0; j <= 9; j++) {
printf("%d ", a[i][j]);
}
printf("\n");
}
}``` Print out the following 10 lines of Yang Hui triangle

```1
1 1
1 2 1
1 3 3 1
1 4 6 4 1
1 5 10 10 5 1
1 6 15 20 15 6 1
1 7 21 35 35 21 7 1
1 8 28 56 70 56 28 8 1
1 9 36 84 126 126 84 36 9 1```
```#include<stdio.h>

void main()
{
int a,i,j;

for (i = 0; i <= 9; i++){
for (j = 0; j <= i; j++) {
if (j == 0 || j == i) {
a[i][j] = 1;
}
else
{
a[i][j] = a[i - 1][j - 1] + a[i - 1][j];
}
}
}
printf("\n");

for (i = 0; i <= 9; i++) {
for (j = 0; j <= i; j++) {
printf("%d ", a[i][j]);
}
printf("\n");
}
}``` Added by Arryn on Mon, 28 Feb 2022 15:48:44 +0200