Programming Forums > Application Development > C

cjaime · Nov 11th, 2005, 11:55 AM

before i start this question i wanna say thanks for all the helpful comments about my switch statement post. i realized however, that in that case my problem was also due to incorrect pointer use. atleast thats what the teacher tells me. the switch statement itself was fine. but im still having a lot of trouble with pointers, i think.
i have this program which requires three different colors to be inputed, each color represents a number, the first two are two digits in a two digit number, and the last one a power of ten. i understand what i need to do but i cant get a proper output from a function.
you see, i started practicing using pointers before i started the rest of the program, and all i want to do is have the program print the scanned variables on the screen. in order to get the hang of it i put the same printf statement inside and outside of the function.
at one point the inside one worked, but the outside one didnt, leading me to believe my pointers were wrong. then, after some fiddling, i cant get either to work.
heres my code. when you input "black brown red" you should get 0, 1, 2.
i appreciate any help.

Quote:

#include<stdio.h>
#include<math.h>
#include<string.h>

/*prototype functions*/
void scan_data(const char *colors[], int *dig1, int *dig2, int *dig3);
int search(const char *arr[], const char *target, int n);

int
main(void)
{
char *colors[10][7] = {"black", "brown", "red", "orange", "yellow", "green", "blue", "violet", "gray", "white"};
int digit1, digit2, digit3;

scan_data(colors, &digit1, &digit2, &digit3);
printf("The numbers should be %d, %d, %d.\n", &digit1, &digit2, &digit3);
return(0);
}

/*This program will get the colors*/
void scan_data(const char *colors[], int *dig1, int *dig2, int *dig3)
{
char color1[7], color2[7], color3[7];

printf("Enter the colors of the resistor's three bands, beginning with\n");
printf("the band nearest the end. Type the colors in lowercase letters\n");
printf("only, NO CAPS.\n");
scanf("%s%s%s", &color1, &color2, &color3);

*dig1 = search(colors, color1, 10);
*dig2 = search(colors, color2, 10);
*dig3 = search(colors, color3, 10);
printf("The numbers should be %d, %d, %d.\n", &dig1, &dig2, &dig3);
}
/*This program will turn the strings into numbers*/
int search(const char *arr[], const char *target, int n)
{
int i,
found = 0,
where;

i = 0;
while(!found && i < n){
if(strcmp(arr[i], target) == 0)
found = 1;
else
++i;
}

if(found)
where = i;
else
where = 10;
return(where);
}

Animatronic · Nov 11th, 2005, 1:52 PM

(Toggle Plain Text)

 char *colors[10][7] = {"black", "brown", "red", "orange", "yellow", "green", "blue", "violet", "gray", "white"};
//should be
const char *colors[10] = {"black", "brown", "red", "orange", "yellow", "green", "blue", "violet", "gray", "white"};

You only need an array of char pointers to point to string literals not a 2d array of pointers. Its also common to mark pointers as const when they point to string literals as string literals will normaly be placed in read-only memmory.

(Toggle Plain Text)

 printf("The numbers should be %d, %d, %d.\n", &digit1, &digit2, &digit3);
 printf("The numbers should be %d, %d, %d.\n", &dig1, &dig2, &dig3);
//should be:
printf("The numbers should be %d, %d, %d.\n", digit1, digit2, digit3);
printf("The numbers should be %d, %d, %d.\n", *dig1, *dig2, *dig3);

printf expects its arguments by value so you need to dereference a pointer and do nothing to the int values.

cjaime · Nov 11th, 2005, 10:59 PM

thank you so much. i been racking my brain trying to figure that out. the damned TA's that are supposed to help the students give these really crappy "hints" then tell us "we wont give you the answer." you are a life saver, now i can finish my program and die happy...ok well maybe without the dying part.

in all honesty though, thank you.

linuxpimp20 · Nov 12th, 2005, 12:26 AM

http://www.daweidesigns.com/pointers.php

check out that site by a resident guru.

Nov 11th, 2005, 1:52 PM	#2
Animatronic Programmer Join Date: Jun 2005 Posts: 99 Rep Power: 4	(Toggle Plain Text) char colors[10][7] = {"black", "brown", "red", "orange", "yellow", "green", "blue", "violet", "gray", "white"}; //should be const char colors[10] = {"black", "brown", "red", "orange", "yellow", "green", "blue", "violet", "gray", "white"}; char colors[10][7] = {"black", "brown", "red", "orange", "yellow", "green", "blue", "violet", "gray", "white"}; //should be const char colors[10] = {"black", "brown", "red", "orange", "yellow", "green", "blue", "violet", "gray", "white"}; You only need an array of char pointers to point to string literals not a 2d array of pointers. Its also common to mark pointers as const when they point to string literals as string literals will normaly be placed in read-only memmory. (Toggle Plain Text) printf("The numbers should be %d, %d, %d.\n", &digit1, &digit2, &digit3); printf("The numbers should be %d, %d, %d.\n", &dig1, &dig2, &dig3); //should be: printf("The numbers should be %d, %d, %d.\n", digit1, digit2, digit3); printf("The numbers should be %d, %d, %d.\n", dig1, dig2, dig3); printf("The numbers should be %d, %d, %d.\n", &digit1, &digit2, &digit3); printf("The numbers should be %d, %d, %d.\n", &dig1, &dig2, &dig3); //should be: printf("The numbers should be %d, %d, %d.\n", digit1, digit2, digit3); printf("The numbers should be %d, %d, %d.\n", dig1, dig2, dig3); printf expects its arguments by value so you need to dereference a pointer and do nothing to the int values.

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Nov 11th, 2005, 10:59 PM	#3
cjaime Newbie Join Date: Nov 2005 Posts: 5 Rep Power: 0	thank you so much. i been racking my brain trying to figure that out. the damned TA's that are supposed to help the students give these really crappy "hints" then tell us "we wont give you the answer." you are a life saver, now i can finish my program and die happy...ok well maybe without the dying part. in all honesty though, thank you.

Nov 12th, 2005, 12:26 AM	#4
linuxpimp20 Hobbyist Programmer Join Date: May 2005 Location: ma Posts: 130 Rep Power: 4	http://www.daweidesigns.com/pointers.php check out that site by a resident guru.

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Programming Forums > Application Development > C

pointers are difficult