In this exercise section of the tutorial we will write some C program.

So, we first have to take the value of n (integer) from the user as input.

Then, we have to check if the value of n satisfies the condition 1 <= n <= 10 i.e., n must be greater than or equal to 1 and n must be less than or equal to 10. So, n can take any value from 1 to 10.

Lets write the C program.

```
/**
* file: hello_world.c
* author: yusuf shakeel
* date: 2010-12-15
* description: hello world program
*/
#include <stdio.h>
int main(void)
{
//variable
int n, i;
//user input
printf("Enter value of n between 1 to 10: ");
scanf("%d", &n);
//check condition
if (n >= 1 && n <= 10) {
//print Hello World
for (i = 1; i <= n; i++) {
printf("Hello World\n");
}
}
else {
printf("Error: Value of n must be between 1 to 10.\n");
}
printf("End of code\n");
return 0;
}
```

Output

```
Enter value of n between 1 to 10: 5
Hello World
Hello World
Hello World
Hello World
Hello World
End of code
```

If we enter some other value of n then we will get an error message.

```
Enter value of n between 1 to 10: 100
Error: Value of n must be between 1 to 10.
End of code
```

The formula to find the volume of a sphere is given below.

`V = (4πr`^{3})/3
where,
V = Volume of the sphere
r = Radius of the sphere

To solve this lets take the PI value as 3.14 so, we can re-write the expression as follows

```
V = (4 * PI * r * r * r) / 3
where,
V = Volume of the sphere
PI = 3.14 approx. value of π
r = Radius of the sphere
```

Lets write the C program.

```
/**
* file: sphere_volume.c
* author: yusuf shakeel
* date: 2010-12-20
* description: volume of sphere program
*/
#include <stdio.h>
#define PI 3.14
int main(void)
{
//variable
float r, volume;
//user input
printf("Enter radius: ");
scanf("%f", &r);
//compute
volume = (4 * PI * r * r * r) / 3;
//output
printf("Volume: %f\n", volume);
printf("End of code\n");
return 0;
}
```

Output

```
Enter radius: 7
Volume: 1436.026611
End of code
```

```
Pattern:
*
* *
* * *
* * * *
* * * * *
* * * * * *
```

Looking at the above pattern we can tell that there are 6 rows and 6 columns.

So, we can write the first for loop for the rows and the second for loop for the column.

Another thing to note is that:

1st row contains 1 star

2nd row contains 2 stars

3rd row contains 3 stars

and so on...

Lets write the program in C.

```
/**
* file: pattern.c
* author: yusuf shakeel
* date: 2010-12-10
* description: patterns program
*/
#include <stdio.h>
int main(void)
{
//variables
int r, c;
for (r = 1; r <= 6; r++) {
for (c = 1; c <= r; c++) {
printf("* ");
}
printf("\n");
}
printf("End of code\n");
return 0;
}
```

Output

```
*
* *
* * *
* * * *
* * * * *
* * * * * *
End of code
```

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