Sorting an Array of Strings in C using functions

Question

#include <stdio.h>
#include <string.h>
void bubble_sort_grades(char [], int); 
int main(void)
{
    int menuswitch=1;
    int amountofstudents;
    int i;
    int z;
    char studentinfo[100];
    char fname[50][100];
    char lname[50][100];
    char grade[50][100];
    printf("Enter Amount of Students: ");
    scanf("%d ", &amountofstudents);
    for (i=0;i<amountofstudents;i++)
    {
        fgets(studentinfo, sizeof(studentinfo), stdin);
        strcpy(fname[i], strtok(studentinfo, " "));
        strcpy(lname[i], strtok(NULL, " "));
        strcpy(grade[i], strtok(NULL, " "));
    }
        while (menuswitch==1)
        {
            int answer;
            printf("Enter 1 for Alphabetical Sort (First Name) \n");
            printf("Enter 2 for Alphabetical Sort (Last Name) \n");
            printf("Enter 3 for Score Sort \n");
            printf("Enter 0 to exit \n");
            printf("Enter choice now: ");
            scanf("%d", &answer);
            if (answer==1)
            {
                bubble_sort_grades(grade,amountofstudents);
                printf("%s\n", grade[0]);
                printf("%s\n", grade[1]);
            }
            if (answer==2)
            {
                printf("In 2 \n");
            }
            if (answer==3)
            {
                printf("In 3 \n");
            }
            if (answer==0)
            {
                printf("Ending Program \n");
                menuswitch=0;
            }
        }
}
void bubble_sort_grades(char grades2[], int amount)
{
    int c, d , t;
    for (c=0; c<(amount); c++)
    {
        for (d=0; d<amount-1; d++)
        {
            if (grades2[c]>grades2[d+1])
            {
                t=grades2[d+1];
                grades2[d+1]=grades2[d];
                grades2[d]=t;
            }
        }
    }
}

Sorry for asking another questions but I need help on bubble sorting. I created a function to bubble sort the grades of students from the input. Yet, when I do this I get only the first grade sorted instead of the array.

   Input:
    John Smith 86
    Victor Jones 76

Output: 68 76

The Wikipedia article has a good explanation of bubble sort. You should be able to implement yours using the examples there. en.wikipedia.org/wiki/Bubble_sort — Jim Mischel
– Jim Mischel, Commented Oct 15, 2013 at 21:46
i want it to be in increasing order 76 then 86 instead its just sorting the first string in the array (86) — Anthony Devoz
– Anthony Devoz, Commented Oct 15, 2013 at 21:51
Just to get this to build, I had to change some of your prototypes to char grade[50][100];. Did it build this way for you? I think the code you have here does not match what you are actually using. — ryyker
– ryyker, Commented Oct 15, 2013 at 21:55

DaoWen · Accepted Answer · 2013-10-15 22:29:12Z

You have two main problems here.

Problem 1: Incorrect array indexing

As @TWhite already pointed out, the parameter for your bubble-sort function has the wrong type. You've declared your arrays to be of type char[50][100], which means it allocates 50*100 characters as a single large block in memory. If your memory for grade is allocated at baseAddr, then grade[0] is at baseAddr+0, grade[1] is at baseAddr+100, grade[2] is at baseAddr+200, etc. If you don't tell bubble_sort_grades the last dimension of your 2D-array, then it has no way calculate these indices. Changing the signature of bubble_sort_grades to void bubble_sort_grades(char[][100], int) would fix that problem.

Problem 2: You're storing c-strings but treating them like ints

The grade array is an array of c-strings (char*). It stores characters, not ints. That means that this line is totally wrong: if (grades2[c]>grades2[d+1]) (Side note: Notice that you're using c instead of d as the first index, which is also an error). If you want to compare strings, you should instead use strcmp, since comparing two char* values will with the > operator just do a pointer comparison. However, using strcmp requires that all the grades be 2 digits (e.g. 05 instead of 5), otherwise the string "9" will be greater than "80". Since the grades are c-strings, that also means t=grades2[d+1] is totally incorrect since you're storing a char* into an int. You'd need to create a temporary buffer char t[100], then use strcpy instead of copying things around by assignment.

I like @chux's suggestion of using a struct. Using structs has the added benefit of automatically (correctly) handling copying the whole struct when you use the = operator. I was going to suggest something similar, and actually suggest using the built-in qsort routine, but I realize this is probably homework and you may not have covered structs yet. In that case, it's probably easier to just change your grade array to store ints instead of c-strings.

chux · Accepted Answer · 2013-10-15 21:59:40Z

2

A number of issues

Instead of

char fname[50][100];
char lname[50][100];
char grade[50][100];

Use structure

typedef struct {
  char fname[100];
  char lname[100];
  char grade[100];
} Student_t;
Student_t Student[50];

Inside bubble_sort_grades(), usestrcmp() to compare names.

void bubble_sort_grades(Student_t Student[], int amount) {
  int c, d;
  for (c = 0; c < (amount); c++) {
    for (d = 0; d < amount - 1; d++) {
      if (strcmp(Student[d].grade, Student[d+1].grade) > 0) {
        Student_t t;
        t = Student[d];
        Student[d + 1] = Student[d];
        Student[d] = t;
      }
    }
  }
}

There area other significant issues, but this should get the OP going.

edited Oct 15, 2013 at 21:59

answered Oct 15, 2013 at 21:45

chux

158k17 gold badges160 silver badges311 bronze badges

3 Comments

dreamlax Over a year ago

Just nitpicking here, but it's a good idea to keep in mind that the _t suffix for types is reserved by POSIX. It's hardly going to matter in this particular case, but liberal use of _t may lead to problems later.

chux Over a year ago

@dreamlax Look like I should check into that. Any reference suggestions?

dreamlax Over a year ago

See section 2.2.2 here. EDIT, updated version here (same restriction applies).

zubergu · Accepted Answer · 2013-10-15 22:09:22Z

1

One issue is your :

void bubble_sort_grades(char [], int);

Should be changed to :

void bubble_sort_grades(char *[], int);

Consider using char *[] for all your arrays.

edited Oct 15, 2013 at 22:09

zubergu

3,7254 gold badges28 silver badges39 bronze badges

answered Oct 15, 2013 at 21:48

TWhite

7372 gold badges11 silver badges33 bronze badges

2 Comments

zubergu Over a year ago

Maybe you meant char (*)[100]?

DaoWen Over a year ago

TWhite: I like your ninja cow icon— or should I say ninnyuu!

Collectives™ on Stack Overflow

Sorting an Array of Strings in C using functions

3 Answers 3

Comments

3 Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

3 Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related