```
/***************************************************
Areas of Circles and Triangles
Write a program that calculates areas of circles
and triangles, where the use chooses which kind of
object he wants to caclulate areas for.
The area of a circle is Pi r^2, where r is the
radius and Pi is approximately 3.14159265358979324.
The area of a triangle is 1/2 b h, where b is the
length of the base, and h is the height.
***************************************************/
#include "si204.h"
int main() {
// Read type of object: circle or triangle
cstring s;
fputs("Do you have a circle or a triangle? ", stdout);
readstring(s, stdin);
// declare this variable outside the blocks, so that it
// can be used afterwards
double area;
// remember, strcmp returns 0 if the strings are equal
if (strcmp(s, "circle") == 0) {
// Compute area of circle
// These variables are only needed inside the block!
double Pi = 3.14159265358979324;
double radius;
fputs("Enter the radius of your circle: ", stdout);
radius = readnum(stdin);
area = Pi * radius * radius;
}
else {
// Compute area of triangle
// These variables are only needed inside this block!
double base;
double height;
fputs("Enter base length: ", stdout);
base = readnum(stdin);
fputs("Enter height: ", stdout);
height = readnum(stdin);
area = 0.5 * base * height;
}
// print out the computed area
fputs("Area equals ", stdout);
writenum(area, stdout);
fputs("\n", stdout);
return 0;
}
```