C outputting variable positions (pointers) instead of actual values [duplicate] - c

Question

This question already has answers here:
How to convert a string to integer in C?
(13 answers)
Closed 6 years ago.
I was working on a class project and I wanted to do a little bit extra and make validation on my data. The problem seems to happen at num1 = num1Input (and num2 = num2Input) where it is getting the location (I assume) instead of the actual input value
int main(void) {
//variables
char num1input[10];
char num2input[10];
int length, i;
int num1 = 0;
int num2 = 0;
int countErrors1 = 0;
int countErrors2 = 0;
bool correct1 = false;
bool correct2 = false;
//--end of variable declarations--//
do {
printf("Please enter a number: ");
scanf("%s", num1input);
length = strlen(num1input);
for (i = 0; i < length; i++) {
if (!isdigit(num1input[i])) {
countErrors1++;
}
}
if (countErrors1 > 0) {
printf("Input is not a number \n");
} else {
correct1 = true;
}
} while (correct1 == false);
num1 = num1input;
do {
printf("Please enter second number: ");
scanf("%s", num2input);
length = strlen(num2input);
for (i = 0; i < length; i++) {
if (!isdigit(num2input[i])) {
countErrors2++;
}
}
if (countErrors2 > 0) {
printf("Input is not a number \n");
} else {
correct2 = true;
}
} while (correct2 == false);
num2 = (int)num2input;
printf("%d %d \n", num1, num2);
int addition = num1 + num2;
int substraction = num1 - num2;
int multiplication = num1 * num2;
float division = num1 / num2;
printf("Addition: %d Subtraction: %d Multiplication: %d Division: %.1e", addition, substraction, multiplication, division);
getch();
}

Answer 1

You cannot convert a string to a number with a cast such as num1 = num1input;. You need to call a library function from <stdlib.h>:
#include <stdlib.h>
...
num1 = atoi(num1input);
But atoi ignores parsing errors. To ensure that overflows are detected, you can use strtol() as follows:
#include <errno.h>
#include <limits.h>
#include <stdlib.h>
...
errno = 0;
char *endp;
long lval = strtol(num1input, &endp, 10);
if (endp == num1input || errno != 0 || lval < INT_MIN || lval > INT_MAX) {
/* parse error detected:
* you could print an error message.
*/
if (lval < INT_MIN) lval = INT_MIN; /* clamp lval as an int value. */
if (lval > INT_MAX) lval = INT_MAX;
}
num1 = lval;
Or if you want to recognize hexadecimal syntax such as 0x10:
num1 = strtol(num1input, NULL, 0);
The same is applicable for num2input.
Note that isdigit(num1input[i]) is potentially incorrect if char is signed and num1input[i] has a negative value. You should write:
isdigit((unsigned char)num1input[i])
Also note that float division = num1 / num2; will compute the integer division and convert the result to a float. If you want the floating point division, you should write:
float division = (float)num1 / num2;
Note finally that it is recommended to use double instead of float for better accuracy.
Here is a corrected and simplified version:
#include <errno.h>
#include <limits.h>
#include <stdlib.h>
#include <stdio.h>
/* simple implementation of strtoi(), inspired by elegant code from chux */
int strtoi(const char *s, char **endptr, int base) {
long y = strtol(s, endptr, base);
#if INT_MAX != LONG_MAX
if (y > INT_MAX) {
errno = ERANGE;
return INT_MAX;
}
#endif
#if INT_MIN != LONG_MIN
if (y < INT_MIN) {
errno = ERANGE;
return INT_MIN;
}
#endif
return (int)y;
}
int main(void) {
char num1input[20];
char num2input[20];
char *endp;
int num1, num2;
for (;;) {
printf("Please enter a number: ");
if (scanf("%19s", num1input) != 1)
return 1;
errno = 0;
num1 = strtoi(num1input, &endp, 10);
if (errno == 0 && *endp == '\0')
break;
printf("Input is not a number\n");
}
for (;;) {
printf("Please enter a second number: ");
if (scanf("%19s", num2input) != 1)
return 1;
errno = 0;
num2 = strtoi(num2input, &endp, 10);
if (errno == 0 && *endp == '\0')
break;
printf("Input is not a number\n");
}
printf("%d %d\n", num1, num2);
int addition = num1 + num2;
int subtraction = num1 - num2;
int multiplication = num1 * num2;
double division = (double)num1 / num2;
printf("Addition: %d Subtraction: %d Multiplication: %d Division: %g\n",
addition, subtraction, multiplication, division);
getch();
}