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POWhy this example is stuck in an infinite loop in C?
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2013-12-29T20:29:49.520
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<p>In the example below, if I enter a character in Mac OS X terminal, the program will get stuck in an infinite loop, printing <code>Please enter a number:</code> line after line and never allowing the user to input anything. What's wrong with this code? What is the fix? I want to change the code in a way that if a number is not entered, the user is prompted with an error message and asked to enter a number again. </p> <pre><code>#include <stdio.h> int main(int argc, const char * argv[]) { int number = 0, isnumber; getagin: printf("Please enter a number:\n"); isnumber = scanf("%i", &number); if(isnumber) { printf("You enterd a number and it was %i\n", number); } else { printf("You did not eneter a number.\n"); goto getagin; } return 0; } </code></pre> <p>Edit: I edited the code after reading the suggestions, and fixed the infinite loop problem. This is not a bad fix for the infinite loop problem, and with a simple for loop I tell C to search for any none numeric character. The code below won't allow inputs like <code>123abc</code>.</p> <pre><code>#include <stdio.h> #include <ctype.h> #include <string.h> int main(int argc, const char * argv[]) { char line[10]; int loop, arrayLength, number, nan; arrayLength = sizeof(line) / sizeof(char); do { nan = 0; printf("Please enter a number:\n"); fgets(line, arrayLength, stdin); for(loop = 0; loop < arrayLength; loop++) { // search for any none numeric charcter inisde the line array if(line[loop] == '\n') { // stop the search if there is a carrage return break; } if((line[0] == '-' || line[0] == '+') && loop == 0) { continue; } // Exculude the sign charcters infront of numbers so the program can accept both negative and positive numbers if(!isdigit(line[loop])) { // if there is a none numeric character then add one to nan and break the loop nan++; break; } } } while(nan || strlen(line) == 1); // check if there is any NaN or the user has just hit enter sscanf(line, "%d", &number); printf("You enterd number %d\n", number); return 0; } </code></pre>
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Why this example is stuck in an infinite loop in C?
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