#include <stdio.h>
#define POPPRICE 50 /*what the pop price is in cents*/
 
char c;
int leftover=POPPRICE; //
int value; // what was entered
 
int main(int argc, char *argv[])
{
        value=(int)argv[1];
        if ((value / 5) != 10)
        {
                printf("Please enter a number of multiples of 5\n");
                printf("%d\n",value);
        }
        else
        {
        printf("The price of pop is %d, cents", POPPRICE);
        printf("Please insert any combination of nickels [N or n],\n");
        printf("dimes [D or d] or quarters [Q or q].\n");
        printf("You can also return your money to you by pressing R or r\n");
        while ((c=getchar())!='e' && (c=getchar())!='E')
        {
                printf("We have not yet exited\n");
                scanf("%d",&value);
        }
}
 
}

if ( sscanf( argv[1], "%d", &integer ) == 1 )
{
     printf( "%d\n", integer );
}

#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
 
int main ( int argc, char *argv[] )
{
  if ( argc > 1 ) {
    long value;
    char *end;
 
    errno = 0;
    value = strtol ( argv[1], &end, 0 );
 
    if ( *end == '\0' && errno == 0 )
      printf ( "Good integer: %ld\n", value );
    else
      fputs ( "Invalid integer format\n", stderr );
  }
 
  return 0;
}

#include <stdio.h>
 
int main ( int argc, char *argv[] ) {
    int integer =  0;
 
    if ( argc > 1 ) {
        if ( sscanf( argv[1], "%d", &integer ) == 1 ) {
           <snip>
        }
        else {
           <snip>
        }
    }
    <snip>
    return 0;
}

int main (int argc, char *argv[])
{
    int value;
 
    value = atoi(argv[1]);
 
    ...
 
}

int main ( int argc, char *argv[] )
{
  /* Make sure argv[1] exists and is not null */
  if ( argc > 1 ) {
    /* Make sure argv[1] is a valid integer */
    if ( try_parse_int ( argv[1] ) ) {
      int value = atoi ( argv[1] );
 
      /* ... */
    }
  }
 
  return 0;
}

#include <ctype.h>
#include <limits.h>
 
int try_parse_int ( const char *s )
{
  /* Base of the conversion */
  const unsigned base = 10;
 
  /* Largest possible value without the least significant digit */
  const unsigned limit = UINT_MAX / base;
 
  /* Least significant digit from the largest possible value */
  const unsigned top_digit = UINT_MAX % base;
 
  unsigned overflow = 0; /* True if integer overflow occurs */
  unsigned sign = 0;     /* Sign of the converted value */
 
  unsigned temp = 0;     /* The intermediate converted value */
  unsigned n = 0;        /* Count of converted digits */
 
  /* Save and skip over the sign if present */
  if ( *s == '-' || *s == '+' )
    sign = *s++ == '-';
 
  /* Build the intermediate value */
  for ( ; isdigit ( *s ); s++, n++ ) {
    unsigned digit = *s - '0';
 
    overflow =  temp > limit
      || ( temp == limit && digit > top_digit );
 
    if ( overflow )
      break;
 
    /* Shift-add by the base */
    temp = temp * base + digit;
  }
 
  if ( n > 0 ) {
    /* A conversion was made; check for overflow */
    if ( overflow
      || ( sign && temp > -INT_MIN )
      || ( !sign && temp > INT_MAX ) )
    {
      /*
        The intermediate actually overflowed,
        or converting it to int would overflow.
        Either way it's an error to the caller
      */
      return 0;
    }
  }
 
  return n > 0 && *s == '\0';
}