Catching the user entering a string when expecting an integer? - c

Question

I am making a program where the user enters two binary numbers and an operation character then I print the output in decimal. I want the while loop to keep the program running until the user enters quit. How can I read if the user enters quit and not an integer value in the scanf? Is there a way to catch this?
#include <stdio.h>
#include <string.h>
int toDecimal(int num);
int main(){
// Define variables
int num1, num2, result = 0;
char op;
char run[4] = "go";
// While loop to rerun program until quit is entered
while(strcmp(run, "quit\n") != 0){
// Reads user input
scanf("%i %c %i", run, &num1, &op, &num2);
printf("\nnum1: %i num2: %i op: %c\n", num1, num2, op);
num1 = toDecimal(num1);
num2 = toDecimal(num2);
printf("\nnum1: %i num2: %i op: %c\n", num1, num2, op);
}
printf("\nGoodbye!\n");
return 0;
}
I believe that I may be able to read everything in as a string and then convert to an integer however I don't know how. Is this a solution I should look into?

Answer 1

How can I read if the user enters quit and not an integer value in the scanf?
There is no good way with scanf(). Instead get user input with fgets() and do not use scanf() until you know why it is bad.
// Read user input
char buf[80]; // Use adequate size input buffer,
while (fgets(buf, sizeof buf, stdin)) {
buf[strcspn(buf, "\n")] = '\0'; // Lop off potential trailing \n
if (sscanf(bufm "%i %c %i", &num1, &op, &num2) == 3) {
printf("\nnum1: %i num2: %i op: %c\n", num1, num2, op);
num1 = toDecimal(num1);
num2 = toDecimal(num2);
printf("\nnum1: %i num2: %i op: %c\n", num1, num2, op);
} else if (strcmp(buf, "quit")== 0) {
break;
} else {
printf("Bad input <%s> ignored\n", buf);
}
}

Answer 2

This is a pretty basic idea , I hope you get the point.You could also use dynamic memory allocation when reading the string.
Basically you read the whole input with fgets and you extract the variables using sscanf.
#include <stdio.h>
#include <string.h>
int main ()
{
int n1,n2;
char arr[1000],oper;
fgets(arr,sizeof(arr),stdin);
while (strcmp(arr,"quit\n")!=0){
if (sscanf(arr,"%d %c %d",&n1,&oper,&n2)==3); /* Scanning for each number and operator and checking input*/
else
printf("wrong input");
/* Code */
fgets(arr,sizeof(arr),stdin);
}
return 0;
}