How to fix binary search for array of strings in C - c

Question

I have a program in C which is supposed to merge 4 string arrays, sort this new list and then find a surname entered by the user. It works up to finding the surname; it says any surname entered is not in the list even if it is.
printf("Please enter the surname you wish to find\n");
gets(sntbf);
while (lf <= rg) {
p = lf + (rg - 1)/2;
int q = strcmp(list[p], sntbf);
if (q == 0) {
printf("This surname is located at elemnent %d \n", p);
z++;
} else if (q < 0) {
rg = p - 1;
} else if(q>0) {
lf = p + 1;
}
}
if (z==0) {
printf("This surname is not in the list \n");
}
Variables and constant values, only one of the original string arrays posted, the rest are identically formatted
#define SIZE 20
#define TOTAL 42
......
char list[TOTAL][SIZE];
char temp[SIZE];
char sntbf[SIZE];
//define miscellaneous integers to be used at various points of this program
int i = 0;
int j = 13;
int k = 27;
int l = 36;
int m = 0;
int n = 0;
int o = 0;
int lf = 0;
int rg = TOTAL-1;
int p;
int z = 0;
//define each class list as an array
char* a[13] = { "Harmon",
"Farrell",
"Ellison",
"Mcknight",
"Palmer",
"Caldwell",
"Mann",
"Townsend",
"Stuart",
"Hull",
"Pham",
"Singleton",
"Holden"
};
.......
Entire program:
//This is a program which will merge 4 lists of names, sort this new
list, and then find a student by searching for their surname
#include
#include
#define SIZE 20
#define TOTAL 42
int main() {
//define a 2d list array to hold the list of names and a temp array to be used when sorting, as well as a char array to hold the surname to be found
char list[TOTAL][SIZE];
char temp[SIZE];
char sntbf[SIZE];
//define miscellaneous integers to be used at various points of this program
int i = 0;
int j = 13;
int k = 27;
int l = 36;
int m = 0;
int n = 0;
int o = 0;
int lf = 0;
int rg = TOTAL-1;
int p;
int z = 0;
//define each class list as an array
char* a[13] = { "Harmon",
"Farrell",
"Ellison",
"Mcknight",
"Palmer",
"Caldwell",
"Mann",
"Townsend",
"Stuart",
"Hull",
"Pham",
"Singleton",
"Holden"
};
char* b[14] = { "Hudson",
"Harolds",
"Christian",
"Ware",
"Benjamin",
"Atkinson",
"Mcpherson",
"Michael",
"Perez",
"Austin",
"Graves",
"Hammond",
"Barry",
"Christensen"
};
char* c[9] = { "Adkins",
"Prince",
"Collins",
"Garrison",
"Skinner",
"Bean",
"Gentry",
"Chambers",
"Armstrong"
};
char* d[6] = { "Berg",
"Douglas",
"Novak",
"Turner",
"Love",
"Fowler",
};
//now merge all the lists into the list array
for(i=0; i<13; i++) {
strcpy(list[i], a[i]);
}
i=0; //reset i to use it again as a counter
for(i=0; i<14; i++) {
strcpy(list[j], b[i]);
j++;
}
i=0;
for(i=0; i<9; i++) {
strcpy(list[k], c[i]);
k++;
}
i=0;
for(i=0; i<6; i++) {
strcpy(list[l], d[i]);
l++;
}
for(m=0; m<TOTAL-1; m++) {
for(n=0; n<TOTAL; n++){
if(strcmp(list[m], list[n])<0) {
strcpy(temp, list[m]);
strcpy(list[m], list[n]);
strcpy(list[n], temp);
}
}
}
for(o=0; o<TOTAL; o++){
puts(list[o]);
}
printf("Please enter the surname you wish to find\n");
gets(sntbf);
while (lf <= rg) {
p = lf + (rg - 1)/2;
int q = strcmp(list[p], sntbf);
if(q = 0) {
printf("This surname is located at elemnent %d \n", p);
z ++;
}
else if(q < 0) {
rg = p - 1;
}
else if(q > 0) {
lf = p + 1;
}
}
if(z == 0) {
printf("This surname is not in the list \n");
}
return 0;
}

Answer 1

There are a number of problems with your program, but the first thing that I noticed is that when copying from list a which has 13 names, your for loop only copies 12:
for(i=0; i<12; i++) {
strcpy(list[i], a[i]);
}
either change "i<12" to "i <= 12" or "i < 13".
Ideally you would not use hard coded numbers at all, instead if you make the last element in each of the smaller lists NULL (0) you could use while loops and use a single int variable to represent both the next insertion point in the merged list and the total number of items in the list.
For example:
const char* a[] =
{"Harmon","Farrell","Ellison","Mcknight","Palmer","Caldwell",
"Mann","Townsend","Stuart","Hull","Pham","Singleton","Holden",0 };
const char* b[] = {
"Hudson","Harolds","Christian","Ware","Benjamin","Atkinson",
"Mcpherson","Michael","Perez","Austin","Graves","Hammond",
"Barry","Christensen",0 };
int sourceIndex = 0;
int destIndex = 0;
while ( a[sourceIndex] != 0 )
{
strcpy( list[destIndex], a[sourceIndex] );
sourceIndex++;
destIndex++;
}
sourceIndex = 0;
while ( b[sourceIndex] != 0 )
{
strcpy( list[destIndex], b[sourceIndex] );
sourceIndex++;
destIndex++;
}
and so on.
Also, your search is handling the bounds (lf & rg) backwards and it should look like this:
lf = 0;
rg = destIndex - 1;
while (lf<=rg) {
p = (rg + lf)/2;
int q = strcmp(list[p], sntbf);
if(q==0) {
printf("This surname is located at elemnent %d \n", p);
z++;
break;
}
else if(q<0) {
lf = p + 1;
}
else if(q>0) {
rg = p - 1;
}
}
if(z==0) {
printf("This surname is not in the list \n");
}