Retaining input values in C? - c

Question

I have asked for the user to enter in several values to calculate an average, however I'd like to also calculate a gradient which uses the inputted values. How do I name these values so I can use them again? Thank you.
Here is what I have thus far:
#include <stdio.h>
int main () {
int n, i;
float num[1000], total=0, mean;
printf("Enter the amount of x-values:");
scanf("%d", &n);
while (n <= 0 || n > 1000) {
printf("Print error. The number should in range of 0 to 1000.\n");
printf("Please try to enter the amount again: ");
scanf("%d", &n);
}
for (i = 0; i < n; ++i) {
printf("%d. Input x-value:", i+1);
scanf("%f", &num[i]);
total += num[i];
}
mean=total/n;
printf("The mean of all the x-values entered is %.2f to 2 decimal places", mean);
{
float num[1000], total=0, mean;
printf("Enter the amount of y-values:");
scanf("%d", &n);
while (n <= 0 || n > 1000) {
printf("Print error. The number should in range of 0 to 1000.\n");
printf("Please try to enter the amount again: ");
scanf("%d",&n);
}
for (i = 0; i < n; ++i) {
printf("%d. Input y-value:", i+1);
scanf("%f", &num[i]);
total += num[i];
}
mean = total / n;
printf("The mean of all the y-values entered is %.2f to 2 decimal places", mean);
return 0;
}
}

Answer 1

Naming the variable is really up to you, but `int gradient[NUM_ELEMENTS]; seems appropriate. It is an array, which also seems appropriate if it's purpose is to assist in finding the gradient from a series of numbers.
Steps could be:
1) use printf to ask user for values, specify spaces or commas between values. You can also specify a limit of values. Example printf("enter 5 numbers separated by commas\n:");
2) use scanf or similar to read values from standard input (the terminal) into the array: scanf("%d,%d,%d,%d,%d", &gradient[0], &gradient[1], &gradient[2], &gradient[3], &gradient[4]);
3) use the array an a function that will compute the gradient.
Simple example:
(where gradient computation, error checking, bounds checking etc. is all left to you)
int get_gradient(int a[5]);
int main(void) {
int gradient[5];
int iGradient=0;
printf("enter 5 numbers separated by commas");
scanf("%d,%d,%d,%d,%d", &gradient[0], &gradient[1], &gradient[2], &gradient[3], &gradient[4]);
iGradient = get_gradient(gradient);
return 0;
}
int get_gradient(int a[5])
{
return [do computation here using array a];
}
Edit:
The above example works only if you know the number of elements at compile time. It uses an int array that has been created on the stack. If you do not know how big of an array you will need until run-time, for example if user input determines the size, then the array size needs to be determined at run-time. One options is to create the variable needed on the heap. (read about stack and heap here) The following uses some techniques different from the simpler version above to get user input, including a function I called get_int(), which uses scanf() in conjunction with strtol(). Here's the example:
int main(void) {
char input[80]={0};
char **dummy={0};
long *gradient = {0};
int iGradient=0;
int arraysize;
int i;
char* fmt = "%[^\n]%*c";
printf("how many numbers will be entered?");
scanf(fmt, input);
arraysize = strtol(input, dummy, 10);
gradient = calloc(arraysize, sizeof(long));
if(gradient)
{
for(i=0;i<arraysize;i++)
{
gradient[i] = get_int();
}
iGradient = get_gradient(gradient, arraysize);
//free gradient when done getting result
free(gradient);
}
return 0;
}
int get_gradient(int *a, int num)
{
int grad = 0, i;
//do something here to compute gradient
return grad;
}
long get_int(void)
{
char input[80]={0};
char **dummy={0};
char* fmt = "%[^\n]%*c";
printf("Enter integer number and hit return:\n");
scanf(fmt, input);
return strtol(input, dummy, 10);
}