Trouble having terminal run program through bash for loop - bash

Question

#!/bin/bash
for i in {10..11}
do
./duffing -a 1 -b -1 -u 0.25 -w -1 -A 0.4 -t $i | ./stroboscopic > $i.data
done
The $i doesn't seem to work in the program parameter line but I get the data files. This is the error
error converting i to a double for max-time:
leftover characters: i
Bad input data
error converting i to a double for max-time:
leftover characters: i
Bad input data
This is where I parse arguments in duffing program :
void parse_args(int argc, char **argv, state_t *state, system_t *system,
simulation_t *simulation, int *read_initial, int *print_final)
{
int ch;
duffing_state_t *duffing = (duffing_state_t *)system->dx_dt_state;
double dtemp;
size_t i;
while (1) {
ch = getopt_long(argc, argv, short_options, long_options, NULL);
if (ch == -1)
break;
switch(ch) {
case 'd':
simulation->dt = safe_strtod(optarg, "time-step");
break;
case 't':
simulation->t_max = safe_strtod(optarg, "max-time");
break;
case 'T':
duffing->T = safe_strtod(optarg, "transient-time");
break;
case 'x':
state->x[0] = safe_strtod(optarg, "x0");
break;
case 'v':
state->x[1] = safe_strtod(optarg, "v0");
break;
case 'm':
system->m = safe_strtod(optarg, "mass");
break;
case 'a':
duffing->a = safe_strtod(optarg, "alpha");
break;
case 'b':
duffing->b = safe_strtod(optarg, "beta");
break;
case 'u':
duffing->u = safe_strtod(optarg, "mu");
break;
case 'w':
duffing->w = safe_strtod(optarg, "omega");
break;
case 'A':
duffing->A = safe_strtod(optarg, "amplitude");
break;
case 'E':
simulation->step_fn = &euler_step;
break;
case 'M':
simulation->step_fn = &midpoint_step;
break;
case 'R':
simulation->step_fn = &rk4_step;
break;
case 'i':
*read_initial = 1;
break;
case 'f':
*print_final = 1;
break;
case '?':
exit(EXIT_FAILURE);
default:
fprintf(stderr, "?? getopt returned character code 0%o ??\n", ch);
}
}
/* convert input from periods to seconds */
simulation->t_max *= 2*M_PI / duffing->w;
duffing->T *= 2*M_PI / duffing->w;
return;
}
I have ran the program straight from the terminal with the -t 10 so I'm pretty confused why the program is refusing to accept the input from the script.