Finish 5_practice.c

5_practice.c

@@ -1,40 +1,70 @@
 #include <stdio.h>	// for printf function
-#include <stdlib.h>	// for memory allocation
+#include <stdlib.h> // for memory allocation
 #include <time.h>	// for time calculation
 #include <math.h>	// for sine and cosine functions
-int main() {
+int main()
+{
 	// Declare all the variables
 	int k, n, N;
 	double *x, *yr, *yi;
 	time_t t;
 
 	// Input the number N
-
-
+	printf("Input the number N : ");
+	scanf("%d", &N);
+
 	// Locate the memory for x, yr, yi;
+	x = (double *)malloc(N * sizeof(double));
+	yr = (double *)malloc(N * sizeof(double));
+	yi = (double *)malloc(N * sizeof(double));
 
 	// Initial setting for x, for example, x[k] = k
-
-
-
-
-	t = clock();	
-	// yr[n]+i*yi[n] = sum(exp(-i 2 Pi k n / N)*x[k], k=0..N-1), n=0..N-1 
-
-
-
-
-
+	for (k = 0; k < N; k++)
+	{
+		x[k] = k;
+		yr[k] = 0;
+		yi[k] = 0;
+	}
 
+	t = clock();
+	// yr[n]+i*yi[n] = sum(exp(-i 2 Pi k n / N)*x[k], k=0..N-1), n=0..N-1
+	for (n = 0; n < N; n++)
+	{
+		for (k = 0; k < N; k++)
+		{
+			yr[n] += cos(2 * M_PI * k * n / N) * x[k];
+			yi[n] -= sin(2 * M_PI * k * n / N) * x[k];
+		}
+	}
 
 	// output the results
 	t = clock() - t;
 	printf("%d ms for discrete Fourier Transform of %d elements\n", t, N);
 
+	printf("x = \n");
+	printf("[ ");
+	for (k = 0; k < N; k++)
+	{
+		if (k % 10 == 0 && k > 1)
+			printf("...\n  ");
+		printf(" %.0f ", x[k]);
+	}
+	printf(" ]\n");
+
+	printf("y = F(x) = \n");
+	printf("[ ");
+	for (n = 0; n < N; n++)
+	{
+		if (n % 5 == 0 && n > 1)
+			printf("...\n  ");
+		printf(" %.2f %+.2fi ", yr[n], yi[n]);
+	}
+	printf(" ]\n");
+
 	// free the memory located by x, yr, yi
-
-
-
+	free(x);
+	free(yr);
+	free(yi);
+
 	return 100;
 }
-