csci-e26                lecture 5 samples                  page 1
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        :::::::::::::: ex1pa.c ::::::::::::::
        /* ex1pa.c: print addresses */
        #include <stdio.h>

        typedef unsigned long ul;

        int main()
        {
             int i,j;
             char c;
             float a;

             i = 2;
             j = i;
             if ( i == j )
                c = 't';

             printf("i=%d, j=%d, c=%c, a=%f\n", i,j,c,a);
             printf("locations are:\n");
             printf("i=%p, j=%p, c=%p, a=%p\n", &i,&j,&c,&a);
             printf("i at %lu, j at %lu, c at %lu, a at %lu\n",
                        (ul)&i,(ul)&j,(ul)&c,(ul)&a);
             return 0;
        }
        :::::::::::::: ex1sa.c ::::::::::::::

        /* ex1sa.c: store addresses */

        #include <stdio.h>

        typedef unsigned long ul;

        int main()
        {
             int i,j;
             char c;
             float a;

             int *p;    /* p holds address of an int */
             int *q;    /* q holds address of an int */
             char *cp;

             p = &i;    /* get address and store it  */
             q = &j;    /* get address and store it  */
             cp = &c;

             i = 3;
             j = i;
             if ( i == j )
                c = 't';

             /* now to print them out */

             printf("i=%d, j=%d, c=%c\n", i,j,c);
             printf("locations are:\n");
             printf("  in hexadecimal:\n");
             printf("    i at %p, j at %p, c at %p\n", p,  q,  cp);
             printf("  in decimal:\n");
             printf("    i at %lu, j at %lu, c at %lu\n", (ul)p,  (ul)q,  (ul)cp);
             printf("    p at %lu, q at %lu, cp at %lu\n", &p,  &q,  &cp);
        }
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csci-e26                lecture 5 samples                  page 3
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        :::::::::::::: ex1dp.c ::::::::::::::

        /* ex1dp.c: dereference pointers */

        #include <stdio.h>

        typedef unsigned long ul;

        int main()
        {
             int i,j;
             char c;

             int *p;    /* p holds address of an int */
             int *q;    /* q holds address of an int */
             char *cp;

             p = &i;    /* get address and store it  */
             q = &j;    /* get address and store it  */
             cp = &c;

             *p = 3;    /* same as: i = 3; */
             *q = *p;   /* same as: j = i; */
             if ( *p == *q )    /* same as if ( i == j ) */
                *cp = 't' ;     /* same as       c = 't'; */

             /* now to print them out */

             printf("i=%d, j=%d, c=%c\n", i,j,c);
             printf("locations are:\n");
             printf("i at %p, j at %p, c at %p\n", p, q, cp);
        }
        :::::::::::::: ex1cp.c ::::::::::::::

        /* ex1cp.c: compare pointers */

        #include <stdio.h>

        typedef unsigned long ul;

        int main()
        {
             int i,j;
             char c = 'x';

             int *p;    /* p holds address of an int */
             int *q;    /* q holds address of an int */
             char *cp;

             p = &i;    /* get address and store it  */
             q = &j;    /* get address and store it  */
             cp = &c;

             *p = 3;    /* same as: i = 3; */
             *q = *p;   /* same as: j = i; */
             if ( *p == *q ){   /* same as if ( i == j ) */
                printf("*p equals *q: values pointed to are equal\n");
                *cp = 't' ;     /* same as       c = 't'; */
             }
             if ( p == q )
                printf("p equals q: p and q point to same location\n");
             else
                printf("p != q: p and q point to different places\n");

             /* now to print them out */
             printf("i=%d, j=%d, c=%c\n", i,j,c);
             printf("locations are:\n");
             printf("i at %p, j at %p, c at %p\n", p, q, cp);
             return 0;
        }
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csci-e26                lecture 5 samples                  page 5
_________________________________________________________________
        :::::::::::::: ex1pf.c ::::::::::::::

        /* ex1pf.c: pass to functions */

        #include <stdio.h>

        void compare(int *, int *);
        void display(int *, char *);

        int main()
        {
             int i,j;
             char c;

             int *p;    /* p holds address of an int */
             int *q;    /* q holds address of an int */
             char *cp;

             p = &i;    /* get address and store it  */
             q = &j;    /* get address and store it  */
             cp = &c;

             *p = 3;    /* same as: i = 3; */
             *q = *p;   /* same as: j = i; */
             if ( *p == *q )
                 c = 't';

             compare(p, q);
             display(p, cp);
        }
        /*
         * compare values AND addrs of two int ptrs
         */
        void compare(int *p1, int *p2)
        {
             if ( *p1 == *p2 )  /* same as if ( i == j ) */
                printf("values of pointees are equal\n");
             if ( p1 == p2 )
                printf("both point to same place\n");
             else
                printf("point to different places\n");
        }
        void display(int *ip, char *cp)
        {
            printf("values are: %d %c\n", *ip, *cp);
            printf("addrs  are %p %p\n",   ip,  cp);
        }
        :::::::::::::: ex2.c ::::::::::::::
        /* ex2.c: arrays */

        #include <stdio.h>

        int main()
        {
                char    m[10] = "hello";
                char    n[]   = "how are you?";

                char    *p, *q;
                p = &m[0];    /* OR p = m */
                              /* name of array is addr of 1st el */
                q = n;

                if ( *p == *q )
                        printf("values are same\n");
                if ( p == q )
                        printf("addresses are same\n");
                else
                        printf("addresses differ\n");

                printf("the char at m is %c\n", *m);
                printf("the string at m is %s\n", m);
                printf("the address of m is %lu\n", (unsigned long) m);
                printf("the address of n is %lu\n", (unsigned long) n);
                return 0;
        }
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csci-e26                lecture 5 samples                  page 7
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        :::::::::::::: ex2ia.c ::::::::::::::
        /* ex2ia.c index into arrays */

        #include <stdio.h>

        int main()
        {
                char    m[10] = "hello";
                char    n[]   = "how are you?";

                char    *p, *q;
                p = &m[0];    /* OR p = m */
                q = n;

                printf("chars in m[2] and m[4] are %c %c\n", p[2], p[4]);
                *q = p[2];
                printf("string at n is %s\n", q);
        }
        :::::::::::::: ex2ao.c ::::::::::::::
        /* ex2ao.c: arithmetic operations */

        #include <stdio.h>

        int main()
        {
                char    m[10] = "hello";
                char    n[]   = "how are you?";

                char    *p, *q;
                p = &m[0];    /* OR p = m */
                q = n;

                printf("chars in m[2] and m[4] are %c %c\n", p[2], p[4]);
                printf("string at n is %s\n", q);

                p++;
                q = q + 3;
                printf("chars in m[2] and m[4] are %c %c\n", p[2], p[4]);
                printf("string at n is %s\n", q);
        }
        :::::::::::::: ex2ae.c ::::::::::::::
        /* ex2ao.c: arithmetic exercises */
        #include <stdio.h>
        /*
            232  236 240  244   248  252  256  260     addrs
           +----+----+----+----+----+----+----+----+----+----+----+----+-----+----+
           |    |    |    | ?  |  ? |  ? |  ? |  ? |    |    |    |    |     |    |
           +----+----+----+----+----+----+----+----+----+----+----+----+-----+----+
                          +---------+
                        p |         |
                          +---------+
                         +---+
                        i| ? |
                         +---+
         */
        int main()
        {
                int     t[5], *p, i;

                p = t;
                for ( i=0 ; i<5 ; i++ ){
                        *p = i ;
                        p++;
                }
                for(i=0; i<5; i++){
                        printf("t[%d] = %d\n", i, t[i]);
                }
                printf("t is at %p, p holds value %p and points to %d\n", t, p, *p);
                printf("(p+2)[0] = %d\n", (p+2)[0]);
                printf("(p-2)[4] = %d\n", (p-2)[4]);
                printf("(p+10)[-8] = %d\n", (p+10)[-8]);
                printf("(p+*p)[*(p+1)] = %d\n", (p+*p)[*(p+1)]);
                return 0;
        }
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csci-e26                lecture 5 samples                  page 9
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        :::::::::::::: strchr.c ::::::::::::::
        #include <stdio.h>

        char *my_strchr(char *s, char c);

        typedef unsigned long ul;

        /*
         * a version of strchr
         */
        #define LEN     100

        int main()
        {
                char    line[LEN];
                char    chr;
                char    *where;

                printf("Enter some text: ");
                fgets(line, LEN, stdin);
                printf("Enter a char: ");
                chr = getchar();

                where = my_strchr(line, chr);
                printf("Line is at %lu, strchr returned %lu\n", (ul) line, (ul) where);
                return 0;
        }

        /* strchr(str, chr) returns address of first instance of chr in str or NULL */
        char *my_strchr(char *str, char chr)
        {
                // search for chr in str, return address of where chr is found
                // or return NULL if not found
                // version1: Indexing
                int     i;
                for ( i = 0 ; str[i] != '\0'; i++ )
                        if ( str[i] == chr )
                                return &str[i];
                return NULL;
                //
                // version2: Using pointers
                //
        }
        :::::::::::::: ex3.c ::::::::::::::
        /* ex3.c: pointers to structs */
        #include <stdio.h>
        #include <string.h>

        struct time
        {
                int     hr, mn;
        };

        struct tstop
        {
                char    stn[20];
                char    dir;
                struct time when;
        };

        void print_event(struct tstop *);

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csci-e26                lecture 5 samples                 page 11
_________________________________________________________________
        int main()
        {
                struct tstop s1, s2;            // get space for the data
                struct tstop *p1, *p2;          // get space to hold addresses

                p1 = &s1;                       // store addresses of data
                p2 = &s2;                       // in pointer variables

                strcpy(s1.stn, "lynn");         // use struct_name.member
                s1.dir = 'i';                   // when using name of struct
                s1.when.hr = 9;
                s1.when.mn = 23;

                strcpy(p2->stn, "salem");       // use struct_ptr->member
                p2->dir = 'i';                  // when using ptr to struct
                p2->when.hr = 9;
                p2->when.mn = 12;

                print_event( &s1 );             // pass address struct s1
                print_event( p2  );             // p2 holds address of struct s2
                return 0;
        }

        /*
         * print out an event: arg is pointer to a train stop event
         */
        void print_event(struct tstop *p)
        {
                printf("station: %s\n", p->stn);
                printf("    dir: %c\n", p->dir);
                printf("   when: %d:%d\n", p->when.hr, p->when.mn);
        }

        :::::::::::::: ex4.c ::::::::::::::
        /* ex4.c: what do I do? */
        #include <stdio.h>

        int main()
        {
                char    veg[4][20];
                int     i;

                strcpy(food[0], "peas");
                strcpy(food[1], "carrots");
                strcpy(food[2], "kale");
                strcpy(food[3], "lettuce");

                for(i=0; i<4; i++)
                {
                        printf("item %d is %s\n", i, food[i]);
                }
                what_do_i_do(veg);
        }

        void what_do_i_do(char a[4][20])
        {
                char    *p[4];
                int     i;

                for(i=0 ; i<4 ; i++)
                {
                        p[i] = &a[4-i];
                }
                for(i=0 ; i<4 ; i++ )
                {
                        printf("in array p, item %d is %s\n", i, p[i] + i);
                }
        }