Convert Char Array to Integer

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char buffer[4];

buffer[0] = command[1];
buffer[1] = command[2];
buffer[2] = command[3];
buffer[3] = '\0';

int  n;
n = atoi(buffer);

OR

char myarray[5] = {'-', '1', '2', '3', '\0'};
int i;
sscanf(myarray, "%d", &i);

OR

char myarray[4] = {'-','1','2','3'};
int i = atoi(myarray);

printf("%d\n",i);