# Array

## Exercise 1

Below is a source code to show 10 data saved in an array. Write the source code and save it as "array1.c". After compilation, confirm by executing it.

```#include <stdio.h>

int main(void) {

int i;
int data[10]={2,3,0,9,12,8,9,-2,7,6};

for (i=0; i<10; i++) {
printf("data[%d] = %d\n", i, data[i]);
}

return (0);
}
```

## Exercise 2

Below is a source code to create an arithmetic progression, save it into an array, and show it. Write the source code and save it as "array2.c". After compilation, confirm by executing it.

```#include <stdio.h>

int main(void) {

int i;
int data[10];

for (i=0; i<10; i++) {
data[i] = 3 * i + 10;
}

for (i=0; i<10; i++) {
printf("data[%d] = %d\n", i, data[i]);
}

return (0);
}
```

## Exercise 3

Write a below source code and save it as "array3.c". After compilation, confirm by executing it with different input.

```#include <stdio.h>

int main(void) {

int i, n;
double data[100];

printf("Input integer or decimal repeatedly\n");
printf("Exit by Ctrl-d\n");

n = 0;
while (scanf("%lf", &data[n]) != EOF) {
n++;
}

for (i=0; i<n; i++) {
printf("data[%d] = %f\n", i, data[i]);
}

return (0);
}
```
```(Execution result)
\$ ./a.out
Input integer or decimal repeatedly
Exit by Ctrl-d
3.4
9.2
-2.54
3
2
^d  <- Exit
data[0] = 3.400000
data[1] = 9.200000
data[2] = -2.540000
data[3] = 3.000000
data[4] = 2.000000
```

## Exercise 4

We want to know a distribution of scores (integer from 0 to 100). Write a below source code and save it as "array4.c". After compilation, confirm by executing it with different input.

Interval (x: score)
0 <= x < 10
10 <= x < 20
20 <= x < 30
30 <= x < 40
40 <= x < 50
50 <= x < 60
60 <= x < 70
70 <= x < 80
80 <= x < 90
90 <= x < 100
x = 100
```#include <stdio.h>
#include <stdlib.h>
#define  N   11

int main(void) {

int i, n, data, num[N];

// Initialization of array
for (i=0; i<N; i++) {
num[i] = 0;
}

// Input data
printf("Input scores repeatedly\n");
printf("Exit by Ctrl-d\n");

n = 0;
while (scanf("%d", &data) != EOF) {

if (data < 0 || data > 100) {
printf("Input scores from 0 to 100\n");
exit(1);
} else {
num[data/10]++;
n++;
}
}

// Show the distribution

for (i=0; i<N-1; i++) {
printf("%3d <= x < %3d : %3d persons\n", i*10, (i+1)*10, num[i]);
}
printf("       x = 100 : %3d persons\n", num[N-1]);

printf("--------------------------------\n");
printf("Total          : %3d persons\n", n);

return (0);

}
```
```(Execution result)
\$
\$ ./a.out
Input scores repeatedly
Exit by Ctrl-d
43
36
84
65
39
81
^d  <- Exit
0 <= x <  10 :   0 persons
10 <= x <  20 :   0 persons
20 <= x <  30 :   0 persons
30 <= x <  40 :   2 persons
40 <= x <  50 :   1 persons
50 <= x <  60 :   0 persons
60 <= x <  70 :   1 persons
70 <= x <  80 :   0 persons
80 <= x <  90 :   2 persons
90 <= x < 100 :   0 persons
x = 100 :   0 persons
------------------------------
Total          :   6 persons
```

## Exercise 5

Below is a source code to show each element of 3x3 matrix. Write a below source code and save it as "array5.c".

```#include <stdio.h>
#define  N  5

int main(void) {

int i, j;
int mat[N][N]={
{2,0,2,0,0},{0,1,0,0,0},{3,0,6,0,0},{0,4,0,1,0},{0,0,0,7,1}};

for (i=0; i<N; i++) {
for (j=0; j<N; j++) {
printf("%3d", mat[i][j]);
}
printf("\n");
}
return (0);
}
```
```(Execution result)
\$ ./a.out
2  0  2  0  0
0  1  0  0  0
3  0  6  0  0
0  4  0  1  0
0  0  0  7  1
```

## Exercise 6

Assuming m x n matrices A and B, sum of A and B are defined as shown in below. Based on Exercise 5, program to calcuate sum of A and B and save it as "array6.c". Assume that both matrices A and B are defined in the source code.

```(Execution result)
\$ ./a.out
A=
2  0  2  0  0
0  1  0  0  0
3  0  6  0  0
0  4  0  1  0
0  0  0  7  1

B=
0  0  0  2  0
2  1  0  0  5
0  0  3  0  0
1  4  0  1  0
2  0  0  0  1

A+B=
2  0  2  2  0
2  2  0  0  5
3  0  9  0  0
1  8  0  2  0
2  0  0  7  2
```

## Exercise 7

Below is a source code to show each character of string. Write the source code and save it as "array7.c". After compilation, confirm by executing it.

```#include <stdio.h>

int main(void)
{
char name[] = "JERS-1/SAR";
int i;

for(i=0; name[i] != '\0'; i++){
printf("%c\n", name[i]);
}

return (0);
}
```
```(Execution result)
\$ ./a.out
J
E
R
S
-
1
/
S
A
R
```

## Exercise 8

Below is a source code to show the length of string. Write the source code and save it as "array8.c". After compilation, confirm by executing it.

```int main(void)
{
char name[] = "JERS-1/SAR";
int i, n=0;

for(i=0; name[i] != '\0'; i++) n++;

printf("n = %d\n", n);

return (0);
}
```

## Exercise 9

In addition to Exercise 8, we want to show calendar of specific three continuous months. Using for-loop, program to show below calendars and save the source code as "for9.c". Input data are (1) day of the week of the first month, and (2) number of days of each month (first, second and third). Be careful that each figure should be right-aligned.

```#include <stdio.h>

int main(void)
{
char name[3][20] = {"English", "Math", "Physics"};
int i;

for(i=0; i<3; i++){
printf("%s\n", name[i]);
}

return (0);

}
```
```(Execution result)
\$ ./a.out
English
Math
Physics
\$
```

## Exercise 10

We want to calculate mean and standard deviation of three subjects (english, math and physics) among students. Equations of mean (upper) and standard deviation (lower) are shown in below.

Using array and referring to execution result, program to meet above requirement and save the source code as "array10.c".

Caution: Calculation of root requires following steps.

1. Write as follows in advance of main function
#include <math.h>
2. In order too calculate root, we can use functions "sqrt()" or "pow()".
a = sqrt(b);
a = pow(b, 0.5);
Be carefult that both variables a and b should be double.
3. Compile as follows.
gcc array11.c -lm
```(Execution result)
\$ ./a.out
Input number of students
5
Student 1's  English 83
Student 1's     Math 65
Student 1's  Physics 78

Student 2's  English 92
Student 2's     Math 89
Student 2's  Physics 100

Student 3's  English 56
Student 3's     Math 67
Student 3's  Physics 62

Student 4's  English 42
Student 4's     Math 65
Student 4's  Physics 52

Student 5's  English 81
Student 5's     Math 63
Student 5's  Physics 55

Mean of  English =  70.8
Mean of     Math =  69.8
Mean of  Physics =  69.4

Std dev of  English =  18.7
Std dev of     Math =   9.7
Std dev of  Physics =  17.7
\$
```

Lessons for C programming
Junichi Susaki, Kyoto University