Welcome to G4EF. Here comes the code
Code:
#define MAX_LINE_SIZE 100

int main()
{
	FILE *fs;
	fs=fopen("xyz.dat","r");
	if(fs==NULL)
	{
		printf("Cannot open source file");
		return 0;
	}

	char *ch = new char[MAX_LINE_SIZE];
	while (fgets( ch, MAX_LINE_SIZE, fs ))
	{
		printf("%s",ch);
		char tmpBufX[MAX_LINE_SIZE];
		char tmpBufY[MAX_LINE_SIZE];
		for(int i = 0;ch[i] != ','; i++)
		{
			tmpBufX[i] = ch[i];
		}
		tmpBufX[i++] = '\n';
		for(int j = 0;ch[i] != '\n'; i++,j++)
		{
			tmpBufY[j] = ch[i];
		}
		tmpBufY[j] = '\n';
		double x = atof(tmpBufX);
		double y = atof(tmpBufY);
	}
	fclose(fs);
	return 0;
}