Initial commit of lecture code

LC12/global_ex1.c

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+/* 
+   This makes global variables look like a good idea
+   
+			THEY ARE NOT - DO NOT USE THEM
+
+*/
+
+#include <stdio.h>
+#include <stdlib.h>
+
+int y,k,ans;							/* Define GLOBAL variables */
+
+void NastyGlobalFunction (void )		/* Define function */
+{
+    ans =  ( y * k );					/* y, k and ans are defined globally above */
+    return ;
+}
+
+int main( void )
+{
+   y = 2;					/* Set value of y */
+   k = 3;					/* Set value of k */
+
+   NastyGlobalFunction();	/* call the function */
+
+   printf("%d multiplied by %d is %d " ,y ,k ,ans );   /* Display values */
+   return 0;
+}

LC12/global_ex2.c

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+/*
+   In this example, we do not have a problem as although
+   we have a global variable 'i', we do not corrupt it in
+   the function
+
+*/
+
+#include <stdlib.h>
+#include <stdio.h>
+
+int i;         /* Nasty global variable ! */
+
+/*
+       This function returns the sum of the number 1->10
+       Note that although we use 'i' it is not defined in
+       the function its self.
+*/
+
+int SumToTen ( void )
+{
+
+	int Result = 0;
+
+	for ( i = 10 ; i >= 0 ; i-- )		// Count down as more effecient
+		Result = Result + i;
+
+	return Result;
+}
+
+/* This is our main function */
+
+int main(void)
+{
+	printf ("\nThe sum of the values 0 to 10 is %d ",SumToTen() );
+	return 0;
+}
+

LC12/global_ex3.c

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+/* 
+
+	This time we have a real problem. We are using the variable 
+	'i' in the main loop to count and again in the function. 
+
+	Thus the function will change the value seen by the 'main'
+	routine - and will cause *Serious* problems
+
+*/
+
+#include <stdlib.h>
+#include <stdio.h>
+
+int i; /* Again, the nasty global variable */
+
+/* 
+
+       This function returns the sum of the number 0 -> i, but
+       summing from the limit back to zero ( to prove a point ! )
+
+       The problem this will cause is that at the end of the routine
+       the value of 'i' will always be '1' which will stop the loop    
+       in 'main' working !
+
+*/
+
+
+int SumToValue ( int Limit )
+{
+
+	int Result = 0;
+	
+       printf("\nIn function ");
+
+	for ( i = Limit ; i > 0 ; i-- )
+		Result = Result + i;
+
+	return Result;
+}
+
+/* 
+   This is our main function - this time we are aiming to print out
+   at table of the sums of values from 1 to 10 
+*/
+
+
+int main( void )
+{
+
+	for ( i =  0 ; i < 10 ; i++ )
+	{
+		printf ("\nThe sum of the values 0 to %d is %d ",i,SumToValue(i));
+	}
+
+	return 0;
+}
+