move exercises, lecture examples, labs into subfolders

Exercises/C14/quadratic_solver.c

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+#include <stdio.h>
+#include <stdlib.h>
+#include <math.h>
+
+int SolveQuadraticEquation(float a, float b, float c, float *x1, float *x2)
+{
+    float d;    // For storing b^2 - 4*a*c
+
+    if ( a == 0)    // Not a quadratie
+    {
+        return -1;
+    }
+
+    // calculate and store b*b-4*a*c for testing ans use later (if OK)
+    d = b*b - 4*a*c;
+
+    if ( d < 0 )
+    {
+        return -1;  // Complex
+    }
+
+    // If we have got to here, we can calculate x1 and x2
+    *x1 = ( -b + sqrt (d)) / (2 * a);  // Note the use of the * before x1 & x2
+    *x2 = ( -b - sqrt (d)) / (2 * a);  // to write to the relevant memory locations 
+
+    // As we got here OK, return 0 to indicate all is OK
+    return 0;
+}
+
+int main (void ) 
+{
+    float A,B,C,x1,x2;
+    int retval;
+
+    printf ("Please enter coefficients A,B and C separated by a space\n");
+    scanf ("%f %f %f", &A, &B, &C);
+
+    // Make use of the function
+    retval = SolveQuadraticEquation(A, B, C, &x1, &x2);
+
+    // Use the retval to determine if we can display the answers or an derror message
+    if ( retval == -1 )
+    {
+        printf ("Not a quadratic\n");
+    }
+    else if (retval == -1)
+    {
+        printf ("The solution is complex - I cannot solve these\n");
+    }
+    else
+    {
+        printf("\nThe solutions are x1=%f, x2=%f", x1, x2);
+    }
+    return 0;   // exit
+}