Having trouble with C pointers - c

Question

First of all, im a begginer C programmer, studying in a university. I need to do a program that is kinda like a data base. Thus far i have made the function to input new data, it works, but compiler shows a few warning and notes, i tried a lot of things, but nothing helped. Here is the code:
#include <stdio.h>
#include <ctype.h>
#include <stdlib.h>
#include <string.h>
struct subjects{
char *subjName[100];
char *lectName[100];
char *lectSurname[100];
double credits;
double studentnum;
}subj;
char subjectname[][100];
char lecturername[][100];
char lecturersurname[][100];
int credits[100];
int students[100];
int newentry=0;
void listInput();
void listEdit();
void listDelete();
void listPrint();
int userChoice();
int main() {
int select;
int r=1;
while(r!=0){
select=userChoice();
switch(select){
case 1:
listPrint();
break;
case 2:
listInput();
break;
case 3:
listDelete();
break;
case 4:
listEdit();
break;
case 0:
r=0;
break;
}
}
return 0;
}
int userChoice(){
int choice,input=0,check;
printf("(1). View all the data\n");
printf("(2). Enter new data\n");
printf("(3). Delete data\n");
printf("(4). Edit data\n");
printf("(0). Exit\n");
printf("-----------------------------\n");
while(input!=1){
printf("Enter your choice\n");
scanf("%d", &choice);
if(choice>4 || choice<0){
printf("Invalid input \n");
}
else
input = 1;
}
return choice;
}
void listPrint(){
for(int i=0; i<newentry; i++){
printf("%d, %s, %s, %s, %d, %d\n",i+1, subjectname[i], lecturername[i], lecturersurname[i], credits[i], students[i]);
}
}
void listInput(){
int i;
char firstLetter,term;
printf("Enter the name of the subject \n");
while(scanf("%s", &subj.subjName)!=1)
printf("Error, subject name must be a text ");
printf("Enter the name of the lecturer \n");
int valid=0;
while(valid!=1){
while(scanf("%s", &subj.lectName)!=1)
printf("Error, lecturer's' name must be a text ");
firstLetter=*subj.lectName;
if(firstLetter>65 && firstLetter<90 && isalpha(firstLetter)){
valid=1;
}
else
printf("Error, lecturer's name must start with a capital letter, try again \nEnter the name of the lecturer \n");
}
valid=0;
printf("Enter the surname of the lecturer\n");
while(valid!=1){
while(scanf("%s", &subj.lectSurname)!=1)
printf("Error, lecturer's surname must be a text ");
firstLetter=*subj.lectSurname;
if(firstLetter>65 && firstLetter<90 && isalpha(firstLetter)){
valid=1;
}
else
printf("Lecturer's surname must start with a capital letter, try again \nEnter the surname of the lecturer \n");
}
printf("Enter the amount of credits in course \n");
while(1){
scanf("%lf", &subj.credits);
if(subj.credits<0 || subj.credits != (int)subj.credits)
printf("Error, amount of credits must be a positive integer, try again \n");
if(subj.credits>0 && subj.credits == (int)subj.credits)
break;
}
printf("Enter the number of students \n");
while(1){
scanf("%lf", &subj.studentnum);
if(subj.studentnum<0 || subj.studentnum != (int)subj.studentnum)
printf("Error, number of students must be a positive integer,try again \n");
if(subj.studentnum>0 && subj.studentnum == (int)subj.studentnum)
break;
}
printf("Added a new entry.\n\n");
strncpy(subjectname[newentry], subj.subjName, 99);
strncpy(lecturername[newentry], subj.lectName, 99);
strncpy(lecturersurname[newentry], subj.lectSurname, 99);
credits[newentry]=subj.credits;
students[newentry]=subj.studentnum;
newentry++;
}
void listDelete(){
printf("33333333333");
}
void listEdit(){
printf("4444444");
}
And the warnings:
In function 'listInput':
96 14 [Warning] assignment makes integer from pointer without a cast
108 14 [Warning] assignment makes integer from pointer without a cast
132 33 [Warning] passing argument 2 of 'strncpy' from incompatible pointer type
79 9 [Note] expected 'const char * restrict' but argument is of type 'char **'
133 34 [Warning] passing argument 2 of 'strncpy' from incompatible pointer type
79 9 [Note] expected 'const char * restrict' but argument is of type 'char **'
134 37 [Warning] passing argument 2 of 'strncpy' from incompatible pointer type
79 9 [Note] expected 'const char * restrict' but argument is of type 'char **
At top level:
14 6 [Warning] array 'subjectname' assumed to have one element
15 6 [Warning] array 'lecturername' assumed to have one element
16 6 [Warning] array 'lecturersurname' assumed to have one element
What can i do to fix those warnings? The program works just fine, but i cant pass if i dont fix the warnings.

Answer 1

Here is a better way to do things
#include <stdio.h>
#include <ctype.h>
#include <stdlib.h>
#include <string.h>
typedef struct{
char *subjName;
char *lectName;
char *lectSurname;
double credits;
double num_students;
}Subject;
typedef struct{
Subject **subjs;
int num_subjs;
}Subjects;
void listInput();
void listEdit();
void listDelete();
void listPrint();
int userChoice();
int main() {
Subjects *subjects = malloc(sizeof(Subjects));
subjects->num_subjs = 0;
subjects->subjs = NULL;
int r=1;
while(r!=0){
int select=userChoice();
switch(select){
case 1:
listPrint(subjects);
break;
case 2:
listInput(&subjects);
break;
case 3:
listDelete();
break;
case 4:
listEdit();
break;
case 0:
r=0;
break;
}
}
return 0;
}
int userChoice(){
int choice,input=0,check;
printf("(1). View all the data\n");
printf("(2). Enter new data\n");
printf("(3). Delete data\n");
printf("(4). Edit data\n");
printf("(0). Exit\n");
printf("-----------------------------\n");
while(input!=1){
printf("Enter your choice\n");
scanf("%d", &choice);
if(choice>4 || choice<0){
printf("Invalid input \n");
}
else
input = 1;
}
return choice;
}
void listPrint(Subjects *subjects){
for(int i=0; i< subjects->num_subjs; i++){
printf("%d, %s, %s, %s, %d, %d\n",i+1, subjects->subjs[i]->subjName, subjects->subjs[i]->lectName, subjects->subjs[i]->lectSurname, subjects->subjs[i]->credits, subjects->subjs[i]->num_students);
}
}
char *getln()
{
char *line = NULL, *tmp = NULL;
size_t size = 0, index = 0;
int ch = 1;
while (ch) {
ch = getc(stdin);
if (ch == '\n')
ch = 0;
if (size <= index) {
size += 1;
tmp = realloc(line, size);
if (!tmp) {
free(line);
line = NULL;
break;
}
line = tmp;
}
line[index++] = ch;
}
return line;
}
int isText(char *str,char *name){
for(int i = 0; i < strlen(str);i++){
if((str[i]<'A' || str[i]>'z') && str[i]!=' '){
printf("Error, %s must be a text \n",name);
return 0;
}
}
return 1;
}
int isNegative(int n){
if(n < 0){
printf("Error, number of students must be a positive integer,try again \n");
return 1;
}
return 0;
}
void listInput(Subjects **p_subjects){
while ( getchar() != '\n' );
Subject *new_subj = malloc(sizeof(Subject));
new_subj->subjName = NULL;
new_subj->lectName = NULL;
new_subj->lectSurname = NULL;
new_subj->credits = 0;
new_subj->num_students = 0;
do{
printf("Enter the name of the subject \n");
new_subj->subjName = getln();
}while(!isText(new_subj->subjName,"Subject name"));
do{
printf("Enter the name of the lecturer \n");
new_subj->lectName = getln();
}while(!isText(new_subj->lectName,"Lecturer's name"));
do{
printf("Enter the surname of the lecturer\n");
new_subj->lectSurname = getln();
//Convert to uppercase
new_subj->lectSurname[0] &= '_';
}while(!isText(new_subj->lectSurname,"Lecturer's surname"));
do{
printf("Enter the number of credits \n");
scanf("%d", &new_subj->credits);
}while(isNegative(new_subj->num_students));
do{
printf("Enter the number of students \n");
scanf("%d", &new_subj->num_students);
}while(isNegative(new_subj->num_students));
(*p_subjects)->subjs = realloc((*p_subjects)->subjs,sizeof(Subject*)*(++(*p_subjects)->num_subjs));
(*p_subjects)->subjs[(*p_subjects)->num_subjs-1] = new_subj;
printf("Added a new entry.\n\n");
}
void listDelete(){
printf("33333333333");
}
void listEdit(){
printf("4444444");
}