I am facing a problem while initializing an array in C. I am trying to take input of a variable 'n' and declare an array marks[n] with its value set to zero. I wrote the following part of the program to do it.
int n,k,e,m,x;
scanf("%d %d %d %d", &n,&k,&e,&m);
int marks[n]={0};
but executing the program generates the following warnings and errors:
prog.c: In function ‘main’:
prog.c:10:6: error: variable-sized object may not be initialized
int marks[n]={0};
^~~
prog.c:10:20: warning: excess elements in array initializer
int marks[n]={0};
^
prog.c:10:20: note: (near initialization for ‘marks’)
This is the whole program:
#include <stdio.h>
int main(int argc, char const *argv[])
{
int t;
scanf("%d",&t);
for (int z = 0; z < t; ++z)
{
int num_candidate,num_seat,num_exam,max_mark,mark_needed;
scanf("%d %d %d %d", &num_candidate,&num_seat,&num_exam,&max_mark);
int marks[num_candidate]={0};
/*gets the total marks of each students. mark of the last exam of the */
/*num_candidate-th student is not taken */
for (int i = 0; i < num_candidate; ++i)
{
for(int j=0;j<num_exam;j++)
{
if (i==num_candidate-1 && j==num_exam-1)
{
break;
}
scanf("%d",&mark_needed);
marks[i]=marks[i]+mark_needed;
}
}
/*sorting*/
for (int i = 0; i < num_candidat-2; i++)
{
for(int j=i; j<num_candidat-2; j++)
{
if (marks[j]<marks[j+1])
{
int temp = marks[j];
marks[j]= marks[j+1];
marks[j+1]=temp;
}
}
}
/*prints the needed marks*/
mark_needed=marks[num_seat-1]-marks[num_candidat-1];
printf("%d\n",mark_needed+1 );
}
return 0;
}
My goal is to take num_candidate=number of candidates, num_seat= number of seats in the school, num_exam=number of exams, max_mark=maximum achievable marks in a single exam.
I want to know how many marks the n-th student would need in his final exam to be admitted. his mark of the last exam is not taken as an input in the program and I want to figure out the least marks he would need in the final exam.
How can I solve it?
From the C Standard (6.7.9 Initialization)
3 The type of the entity to be initialized shall be an array of
unknown size or a complete object type that is not a variable length
array type.
So instead of this declaration with an initializer
int marks[n]={0};
use
int marks[n];
memset( marks, 0, n * sizeof( int ) );
Pay attention to that n may not be equal to zero.
Related
This algorithm is a linear search algorithm that finds the desired value. But when I compile this code, gives the segmentation fault in if(dizi[i]==aranan) this line. How can I solve this ?
#include <stdio.h>
int N,i,aranan;
int ArrayBastir(int *dizi,int N)
{
printf("My numbers\n");
for(int i =0; i<N;i++)
{
printf("%d\n", dizi[i]);
}
}
int findValue()
{
printf("The value you want to search");
scanf("%d",&aranan);
}
int Output(int *dizi,int N,int aranan)
{
for(int i =0; i<N;i++)
{
if(dizi[i]==aranan)
{
printf("%d number %d. found in queue \n", aranan,i+1);
}
}
}
int main() {
int N;
int aranan;
printf("Please enter how many numbers you want to enter");
scanf("%d", &N);
int dizi[N];
for(int i =0; i<N;i++)
{
scanf("%d", &dizi[i]);
}
ArrayBastir( dizi, N);
findValue(aranan);
Output(*dizi,N,aranan);
return 1;
}
Linear Search algorithm
You have two objects defined as:
int aranan;
Once is defined at file scope (a global), and one is defined within the scope of main.
When findValue(aranan) is called, a copy of the uninitialized value of aranan within the scope of main is passed to findValue. findValue is lacking a prototype, having not declared its arguments, so this is ignored.
findValue scans a value into the file scope aranan, but when Output(*dizi, N, aranan) is called it uses the value of aranan defined within main. aranan within main was never initialized, and thus this causes Output to search for an indeterminate value.
Additionally, *dizi is an int, when Output expects an int * as its first argument.
ArrayBastir and Output are also defined as each returning an int, which they do not do.
You should not ignore the return value of scanf, as it indicates the number of successful conversions, or a negative value on failure (EOF). In a program this small, you can get away with writing a simple wrapper function for reading integers, that just exits the program if the user enters something invalid.
main returning nonzero generally indicates your program failed. main is special - it is the only non-void function where you can omit a return statement. If main reaches the end of execution without an explicit return, it is treated as though it returned 0.
The issues above can be mitigated by avoiding the use of global variables, and by turning up your compilers warning level to catch obvious type mismatches.
For GCC or Clang, use -Wall -Wextra, and possibly -Werror.
For MSVC, use /Wall, and possibly /Wx.
Minimally refactored:
#include <stdio.h>
#include <stdlib.h>
int get_int(void)
{
int x;
if (1 != scanf("%d", &x)) {
fprintf(stderr, "Invalid input.\n");
exit(EXIT_FAILURE);
}
return x;
}
void ArrayBastir(int *dizi, int N)
{
printf("My numbers\n");
for (int i = 0; i < N; i++) {
printf("%d\n", dizi[i]);
}
}
void Output(int *dizi, int N, int aranan)
{
for (int i = 0; i < N; i++) {
if (dizi[i] == aranan) {
printf("Found <%d> at position %d.\n", aranan, i);
}
}
}
int main(void)
{
printf("Please enter how many numbers you want to enter: ");
int N = get_int();
int dizi[N];
for (int i = 0; i < N; i++) {
dizi[i] = get_int();
}
ArrayBastir(dizi, N);
printf("Enter the value you want to search for: ");
int aranan = get_int();
Output(dizi, N, aranan);
}
in my first year University class we have just started fiddling with arrays and on the worksheet I was given this code, which doesn't seem to work. I've been scanning and looking for a problem but nothing seems to fix it. Here is my code...
#include <stdio.h>
#include <stdbool.h>
int main(){
int size = 10;
float suspect[size]; //Declaring suspect array
int sizeR = 3;
int sizeC = 10;
float criminals[sizeR][sizeC]; //Declaring criminals array
//Read 10 input values into suspect array from keyboard
printf("Enter the 10 chromosomes of the suspect separated by spaces: \n");
for (int i = 0; i < size; i++)
scanf(" %f", &suspect[i]);
//Read multiple profiles of 10 values into criminals array from the keyboard
for (int i = 0; i < sizeR; i++){
printf("Enter the 10 chromosomes of the %dth criminal: \n", i+1);
//Read 10 input values of a criminal into criminals array from the keyboard
for (int j = 0; j < sizeC; j++)
scanf(" %f", &criminals[i][j]);
}
//Match two profiles
bool match = true;
for (int i = 0; i < size; i++)
if(suspect[i] != criminals[i]) //Error is in this line
match = false;
//Display matching result
if (match)
printf("The two profiles match! \n");
else
printf("The two profiles don't match! \n");
return 0;
}
And when I run this code, I am returned with:
error: invalid operands to binary expression ('float' and 'float [sizeC]')
With the error being pointed to the != in the matching two profiles part. Excuse me if the solution is simple, coding is relatively new to me and I am struggling to find the solution to this particular problem using Google.
In this if statement
if(suspect[i] != criminals[i]) //Error is in this line
the expression criminals[i] is implicitly converted to the type float * because the original type of the expression before the conversion is float[sizeC].
And moreover the expressions suspect[i] has the type float. That is there are compared an object of the type float with a pointer of the type float * that does not make a sense.
So the compiler issues the error message.
If you are going to compare the array suspect with elements of the two-dimensional array criminals you should use one more inner for loop.
This a dot_product function of 2 vectors of the same length.
I don't understand how to build the array because how the machine will know which input goes to which input (for example i want a={1,2,3} but the input of 123 will come a[0]= 123)...
How do I make end of array[index] input and how do I make end of the whole array.
#include <stdio.h>
#include <stdlib.h>
#define MAXINPUT 100
int dot_product(int v[], int u[], int n)
{
int result = 0;
int i;
for (i=0; i < n; i++)
result += v[i]*u[i];
return result;
}
int main(){
int v1[MAXINPUT];
int v2[MAXINPUT];
int count = 0
int i,print;
printf(" first vector:");
for(i=0;i<MAXINPUT;i++){
scanf("%d", &v1[i]);
count +=1;
}
printf(" second vector:");
for(i=0;i<MAXINPUT;i++)
scanf("%d", &v2[i]);
print = dot_product(v1, v2, count);
printf("v1*v2:%d",print);
return 0;
}
The first problem I observe here is with
count +=1;
where count is an uninitialized automatic local variable, which makes it's initial value indeterminate. Attempt to use that value invokes undefined behavior.
You should be initializing count to 0.
That said, here, you're depending on the user to input the second array with exact same dimension of that of the first one. In case that does not happen, your program will blow up, as you did not initialize the arrays, again.
So i have this type of problem. How to make an array 1*x and then sum up its digits together. I wrote down something like this for now. Any ideas? Thank you.
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
/* run this program using the console pauser or add your own getch, system("pause") or input loop */
int main(int argc, char *argv[])
{
int a,i,w,j,m;
int s[a];
printf("How many digits do you want to sum up\n");
scanf("%d",&a);
for(i=0;i<a;i++)
{
printf("Enter numer %d: ",i);
scanf("%d",&s[i]);
}
for(j=0;j<a;j++)
{
m=s[j]+s[j++];
}
printf("\n %d",m);
return 0;
}
The problems of your code are:
int a;
int s[a];
Here a is uninitialized.So,array size is unknown which is incorrect.And,instead of this
m=s[j]+s[j++];
you should do like this :
m += s[j];
One more thing,you have initialize m = 0 before starting to add.
I've Changed your program to this:
#include <stdio.h>
int main(int argc, char *argv[]) {
int a,i,m = 0;
//First get the array size
printf("How many digits do you want to sum up\n");
scanf("%d",&a);
//Then declare the array with the size (a)
int s[a];
for(i = 0; i < a; i++){
printf("Enter numer %d: ",i);
scanf("%d",&s[i]);
m += s[i];
}
printf("\n %d",m);
return 0;
}
Using uninitialized variable is undefined behaviour.
int s[a];
The above statement defines an array s of size a but the value of a is unpredictable since it is uninitialized and contains garbage. The size of the array must be known when it defined and it remains the same throughout its lifetime. You cannot resize your array by changing the value of a here. You can use dynamic memory allocation using malloc.
Further, the following statement again invokes undefined behaviour -
m=s[j]+s[j++];
That's because it violates the the following rule stated in the C99 standard §6.5 ¶2
Between the previous and next sequence point an object shall have its
stored value modified at most once by the evaluation of an expression.
Furthermore, the prior value shall be read only to determine the value
to be stored.
I'm working on a homework assignment and I've hit a brick wall. I think I have all of the code that I need, I just need to get the program to compile. The object of the assignment is
Create a structure to hold student names and averages. The structure should contain a first name, last name and an integer grade average.
Then:
Write a program that will do the following:
1.) Create an array of pointers to these student structures.
2.) Prompt the user for names and averages.
3.) After you get the student’s information use malloc to provide the memory to store the information.
4.) Place the address of the student, returned by malloc, into the pointer array.
5.) AFTER the user indicates there are no more students:
Search the data entered and find the highest and lowest grade
average.
a)Print the name and grade for the highest grade
b)Print the name and grade for the lowest grade
c)Print the average of all grades entered
Here is my code:
#include "stdafx.h"
#include <string.h>
#include <stdlib.h>
#define SIZE 25
int enterStudents (int ePointArray[SIZE]);
void searchData (int *sPointArray, int *sHigh, int *sLow);
int calculateAvg (int, int *avgPointArray);
void printData (int, int *pHigh, int *pLow);
struct student
{
char firstName[20];
char lastName[20];
int average;
};
int main()
{
int pointArray[SIZE], high[3], low[3];
int i = 0, studentCounter, avgGrade;
for (i = 0; i < SIZE; i++)
pointArray[i] = 0;
studentCounter = enterStudents(pointArray);
searchData(pointArray, high, low);
avgGrade = calculateAvg(studentCounter, pointArray);
printData(avgGrade, high, low);
return 0;
}
int enterStudents (int ePointArray[SIZE])
{
char tempFname[20], tempLname[20], yesNo[2] = "y";
int tempAvg, counter = 0;
int *studPtr;
struct student aStud={"\0", "\0", 0};
while( counter < SIZE && strcmp(yesNo, "y")==0)
{
printf(" Enter first name: ");
scanf("%s", tempFname);
printf(" Enter last name: ");
scanf("%s", tempLname);
printf(" Enter grade average:");
scanf("%d", tempAvg);
strcpy(aStud.firstName, tempFname);
strcpy(aStud.lastName, tempLname);
aStud.average = tempAvg;
studPtr = malloc(sizeof(struct student));
ePointArray[counter] = *studPtr;
counter++;
printf("/n");
printf(" Do you have more students? yes or no:");
scanf("%s", yesNo);
}
return counter;
}
void searchData (int sPointArray[SIZE], int sHigh[3], int sLow[3])
{
int searchCounter = 0;
while( searchCounter = 0)
{
if( *sPointArray[searchCounter].average > *sPointArray[searchCounter+1].average)
{
sHigh[0] = &sPointArray[searchCounter].firstName;
sHigh[1] = &sPointArray[searchCounter].lastName;
sHigh[2] = &sPointArray[searchCounter].average;
}
if( *sPointArray[searchCounter].average < *sPointArray[searchCounter+1].average)
{
sLow[0] = &sPointArray[searchCounter].firstName;
sLow[1] = &sPointArray[searchCounter].lastName;
sLow[3] = &sPointArray[searchCounter].average;
}
searchCounter++;
}
}
int calculateAvg( int totalStudents, int avgPointArray[SIZE])
{
int sum = 0;
int avgCounter;
double overallAvg;
for( avgCounter = 0; avgCounter < totalStudents; avgCounter++)
sum = sum + *avgPointArray[avgCounter].average;
overallAvg = sum/totalStudents;
return overallAvg;
}
void printData (int pAverage, int pHigh[3], int pLow[3])
{
printf(" Highest Grade: %s %s %d", pHigh[0], pHigh[1], pHigh[3]);
printf("/n");
printf(" Lowest Grade: %s %s %d", pLow[0], pLow[2], pLow[3]);
printf("/n");
printf(" Average Grade: %d",pAverage);
}
The main chunk of problems come from the searchData function. In the if statements, every occurrence of *sPointArray and &sPointArray is underlined in red and the error reads
"Error: expression must have class type"
The same thing also happens in the calculateAvg function with *avgPointArray in the for loop. I know that the error is a fairly common problem for noobie C programmers (i.e myself) and that it generally has to do with writing the code as a function instead of a statement or something like that, but I can't for the life of me find where I have went wrong. Any help would be highly appreciated. I've been working at this for so long my vision is blurring.
Also, for anyone who solves this in like two seconds and wants proof that I'm a true idiot, there is an error in the enterStudents function where it says StudPtr = malloc(sizeof...). The error shows under the assignment symbol and says
"Error: a value of type "void*" cannot be assigned to an entity of type "int*".
I understand this concept in theory, but some advice for how to fix it would be highly appreciated.
Thank you in advance for any help.
You declare the sPointArray as an array of integers, but use it as an array of structures.