C: While loop exit condition, using fgets for input

As others have said, you need to compare strings with strcmp, instead of !=, as this is incorrect in C.

I also suggest checking the return value of the void* pointer from malloc, as this is good practice to do when allocating space for a dynamic array on the heap.

You also don't need to cast the return value from malloc() .

You can simply write:

char *bnumber = malloc(10 * sizeof *bnumber); 

instead of:

char *bnumber = (char *) malloc(10 * sizeof(char *)); //Note 

I also saw that you included math.h as one of your headers. There is no need for that header because you aren't using any of it's functions.

I also added some extra error checking in this example, as it will help prevent bugs in the program.

here is the code:

#include <stdio.h> #include <stdlib.h> #include <string.h> #define BUFFSIZE 10 int convertbinary(char *binarynumber); int main(void) { int binaryreturn; char *bnumber; size_t currsize = BUFFSIZE, len; const char *quit = "q"; bnumber = malloc(currsize * sizeof *bnumber); if (!bnumber) { printf("Cannot allocate memory!\n"); exit(EXIT_FAILURE); } printf("Enter binary byte or type q to quit: "); while (fgets(bnumber, currsize, stdin) != NULL) { len = strlen(bnumber); if (len > 0) { if (bnumber[len-1] == '\n') { bnumber[len-1] = '\0'; } else { printf("Buffer Exceeds length of %d\n", BUFFSIZE); exit(EXIT_FAILURE); } } if (!*bnumber) { printf("No number entered.\n"); printf("\nEnter binary byte or type q to quit: "); } else { if (strcmp(bnumber, quit) == 0) { printf("Goodbye\n"); break; } binaryreturn = convertbinary(bnumber); printf("binary number = %d\n", binaryreturn); printf("\nEnter binary byte or type q to quit: "); } } free(bnumber); bnumber = NULL; return 0; } int convertbinary(char *binarynumber) { int val = 0; while (*binarynumber != '\0') { val = 2 * val + (*binarynumber++ - '0'); } return val; }