int main(int argc, char **argv)
{
 while(1) {
char buffer[400];
char str;

if(strcmp(argv[1],"start") == 0 )
    { printf("myshell: process has started n");
            int i=0;
            while (str = strtok(buffer," ") == NULL) {
            argv[i] = str;  //**This line causes the warning!

...
int i=0;
str = strtok(buffer, " ");
do {
    argv[i] = str;  //**This line causes the warning!
    ...
} while (str = strtok(NULL, " ") != NULL);