Why does the value of sum changes after for loop in the following code even after I have initialised it as 0 in CodeBlocks?
int main()
{
int a[5], i, sum;
sum= 0; // value of sum is not changed after this.
printf("\nSum=%d", sum);
for( i=1; i<6; i++)
{
printf("\n\nInput %d: ", i);
scanf("%d", &a[i]);
printf("Sum test=%d", sum);
}
printf("\n\nSum=%d", sum); // why does it changes?
return 0;
}
sum never changes because you never modify it.
Furthermore, you have undefined behavior because the loop index is off by one, so you make scanf() write beyond the end of the array arr, which might by coincidence be the location where sum is stored, this would explain why you get Sum=4, the value of the last input.
C arrays are 0 based: use this:
for (i = 0; i < 5; i++)
You must also include the required standard header files and test the return value of scanf() to avoid undefined behavior on invalid input.
Here is a corrected version:
#include <stdio.h>
int main() {
int a[5], i, sum;
sum = 0;
printf("Sum=%d\n", sum);
for (i = 0; i < 5; i++) {
printf("\nInput %d: ", i);
if (scanf("%d", &a[i]) != 1)
break;
sum += a[i];
printf("Sum test=%d\n", sum);
}
printf("\nSum=%d\n", sum);
return 0;
}
Because you are looping over 1 to 6! And rewrite the value of sum here. To avoid this, you should iterate over the scope of the array, from index 0 to 4.
You should be aware that as the memory of sum is adjacent to the allocated memory of the array such a thing is happened, and it is not a rule!
array index starts with 0 so arr[5] is not allocated and the value you entered is given to sum
if atlast you give it as input 6 then the sum value is 6
Related
The elements of the array have to be taken as input from the user. Here I am using an array of size 10. I am getting the sum as 0 if I initialized it with sum = 0; while declaring, and if I didn't, I am getting a garbage value.
Here is the code:
#include <stdio.h>
int main(void)
{
int barray[10], i=0, sum=0;
for(i=0;i<10;i++ ){
printf("Enter the value for barray[%d] element of the array : ",i);
scanf("%d", &barray[i]);
}
while(i >=0 && i<10)
{
sum += barray[i];
i++;
}
printf("The sum of the elements of the array is %d", sum);
}
The problem with your code is that i is not a variable declared in the scope of the for loop but in the scope of main, so when the for loop is done i=10 and then the contents of the while loop are skipped as the condition for i to be greater than 0 and less than 10 are never met.
To fix this you should set i to zero after the for loop
scanf("%d", &barray[i]);
}
i = 0; // add this
while(i >=0 && i<10)
{
or change the while loop to a for loop like the first one. Though I would recommend as good practice and for cleaner code to declare the iterator variable inside the context of the for loop unless you need to access it outside of it, like so.
int main(void)
{
int barray[10], sum=0;
for (int i = 0; i < 10; i++) {
printf("Enter the value for barray[%d] element of the array : ", i);
scanf("%d", &barray[i]);
}
for (int i = 0; i < 10; i++) {
sum += barray[i];
}
printf("The sum of the elements of the array is %d", sum);
}
I'm new to C and need some help to understand how this piece of code works. I know that it reads the values that the user writes, puts them into an array, and then prints them out.
But I don't understand why I need two "counters" (i and j) to do this. Can someone help me to figure it out?
#include<stdio.h>
int main ()
{
int A[5];
int i=0;
int j=0;
while (i < 5)
i++;
printf("Enter your %d number\n", i);
scanf("%d", &A[i]);
}
while (j < 5)
{
j++;
printf ("\n%d\n", A[j]);
}
}
Technically, what you have aren't two counters, but two loops. If you wanted, to, you could just reuse i for the second loop as well, by doing something like this:
while (i < 5)
i++;
printf("Enter your %d number\n", i);
scanf("%d", &A[i]);
}
i = 0;
while (i < 5)
{
i++;
printf ("\n%d\n", A[i]);
}
As for why you have two loops, the reason is simple. The first loop (using i in your code), reads the 5 integers into the array A. After the first loop concludes, your array A holds the 5 int values, which you could've used however you wanted. In your case, you want to print those values. So what you do is use a loop for looping over the array elements and printing the values to the screen, one by one.
You don't need it, you can simply reset the first and reuse it. However you must increment your index only after having using it otherwise you will overflow the limit of the array :
#include<stdio.h>
int main ()
{
int A[5];
int i=0;
while (i < 5) {
printf("Enter your %d number\n", i);
scanf("%d", &A[i]); // the last must be 4 not 5
i++; //<== increment here
}
i=0;
while (i < 5)
{
printf ("\n%d\n", A[i]); //idem
i++;
}
}
I was writing a C program to find inversions in an array. The program compiles smoothly but as soon as I run it, it displays a garbage value where I take the array as a input. The program is given below:
#include <stdio.h>
#include <stdlib.h>
int checkInversions(int arr[], int n) {
int i, j, inverse_count = 0;
for (i = 0; i < n - 1; i++) {
for (j = i + 1; j < n; j++) {
if (arr[i] > arr[j]) {
inverse_count++;
}
}
}
return inverse_count;
}
int main() {
int arr[10], i, n;
printf("Enter the elements of the array: %d");
for (i = 0; i <= 10; i++) {
scanf("%d", &arr[i]);
}
n = sizeof(arr) / sizeof(arr[0]);
printf("\n The inverse is: %d", checkInversions(arr, n));
return 0;
}
Now, when the statement Enter the elements of the array: is displayed, just beside that is a garbage value like 623089. I am able to take the input but the result is not correct. What is the cause of this? Any help in this regard will be appreciated.
You are calling printf with a format specifier for %d and nothing passed to satisfy the variable expected by the format string. This is undefined behavior.
What you meant to do was merely:
printf("Enter the elements of the array: ");
Also, since arr has 10 elements, you iterate through it as such:
for(i = 0; i < 10; i++)
You don't need to use sizeof to determine the size of the array since you already know it; it's 10.
I think you are missing the variable that should populate the %d on the printf.
Try taking out the %d on the printf call so it ends up like:
printf("Enter the elements of the array: ");
Or assign the corresponding variable to display with that "%d", like this:
printf("Enter the elements of the array: %d", variable);
Check if that helps!
Your problem is printf("Enter the elements of the array: %d");. You tell the program that you want to print an integer, but you do not specify which integer that is. Remove the %d and the garbage value will be gone, like this: printf("Enter the elements of the array: ");
My sorting program results in a "segmentation fault 11":
#include <stdio.h>
int main()
{
// Asking user for number of inputs in an array
int n;
do {
printf ("enter the number of intigers you want to sort\n");
scanf("%d",&n);
}while (n<=1);
int sort [n];
printf ("please enter %d numbers\n",n);
for (int i=0; i<n; i++) {
scanf("%d",&sort[i]);
}
printf("you entered\n ");
for (int i=0; i<n; i++) {
printf(" %d ",sort[i]);
}
printf("\n");
int k,c,i,x;
for (i=0;i<n;i++) {
if (sort[i]<sort[i-1]){
k=i-2;
while (sort[k]>sort[i]){
k--;
}
k++;
x =sort[i];
c=i;
for (c=i;c>k;c++){
sort[c-1]=sort[c];
}
sort[k]=x;
}
}
printf ("Sorted numbers :-\n");
for (int i=0; i<n; i++) {
printf ("%d ",sort[i]);
}
printf ("\n");
return 0;
}
Now I have looked up the internet and found that it is caused because a variable has value that exceeds the system's memory limit. But cannot understand that concept.
for (i=0;i<n;i++)
{
if (sort[i]<sort[i-1])
You are accessing array out of its bounds.Maybe you want to start your loop from 1.Also
k=i-2;
while (sort[k]>sort[i])
will access index beyond 0 for example if i is 0 or 1 or 2
k = i - 2; looks unstable for low values of i.
sort[i - 1] is undefined when i is zero.
The thing causes the behaviour of sort[k] to be undefined.
Moral of the story: check all the array indexes before attempting to retrieve an array element. Your debugger will help you here.
In addition to all said before:
c=i;
for (c=i;c>k;c++){
sort[c-1]=sort[c];
}
sort[k]=x;
i can be 0 -> c can be 0 -> sort[c-1] would also result in accessing array out of bounds.
There is no need to initialize c=i twice. It is enough to do it in the loop-declaration
I'm trying to make a one-month calendar that prints the sum of the last row of days.
The output of this is correct for the calendar, but the sum keeps printing out that it's 0. For an input of 3=day_of_week and 30=days_in_month, the sum should be 26+27+28+29+30 = 140
Thanks.
int main() {
int day_of_week, days_in_month, i, row=1, array[31], sum=0, a;
printf("Enter the day of the week 1=sun, 2=mon, 3=tue, 4=wed, 5=thurs, 6=fri, 7=sat\n");
scanf("%d", &day_of_week);
printf("Enter the number of days in this month:\n");
scanf("%d", &days_in_month);
for (i=0; i<3*day_of_week; i++)
printf(" ");
for (i=1; i<=days_in_month; i++) {
printf("%3d", i);
array[i] = i;
day_of_week++;
if (day_of_week%7==0){
printf("\n");
}
}
printf("\n");
for (a=days_in_month; a>=(days_in_month-(7-day_of_week)); a--)
sum+=array[a];
printf("sum of last row is %d\n", sum);
return 0;
}
I don't understand why you are doing ++day_of_week,
something like this should work better:
int main()
{
int day_of_week, days_in_month, i, row=1, array[31], sum=0, a;
printf("Enter the day of the week 1=sun, 2=mon, 3=tue, 4=wed, 5=thurs, 6=fri, 7=sat\n");
scanf("%d", &day_of_week);
printf("Enter the number of days in this month:\n");
scanf("%d", &days_in_month);
for (i = 0; i < 3 * day_of_week; i++)
printf(" ");
for (i = 1; i <= days_in_month; i++)
{
printf("%3d", i);
array[i] = i;
if (i % 7 == 0)
printf("\n");
}
printf("\n");
for (a=days_in_month; a>=(days_in_month-(7-day_of_week)); a--)
sum+=array[a];
printf("sum of last row is %d\n", sum);
return 0;
}
You have
for (a=days_in_month; a>=(days_in_month-(7-day_of_week)); a--)
but day_of_week does not remain constant in your program and changes before with this statement:
day_of_week++;
Use a second variable to increment and do not modify day_of_week after scanf.
One problem is here:
for (i=1; i<=days_in_month; i++) {
printf("%3d", i);
array[i] = i;
day_of_week++;
if (day_of_week%7==0){
printf("\n");
}
}
You are allowing day_of_week to go out of range. Your code expects that value to be no more than 7. This loop will result in that variable being set to the value the user entered plus (days_in_month - 1). In your final for loop, the statement 7 - day_of_week will likely be negative, which will throw the rest of your code off.
You are sort of checking for overflow when you test the variable modulo 7 and print a newline. When you do that, set day_of_week = 0 as well.
Also, calculate (days_in_month-(7-day_of_week)) and store it in a temporary variable as soon as you get the input from the user. Since you're manipulating these variables inside your code, your final for loop probably isn't using the values that you think it's using. Alternatively, don't modify the variables that you use for user input and create other variables to use as temporaries.