[intv] string to int

#include <stdio.h>
//Obj: Convert a String to Int
//Compile as: gcc -o test test.c

int strtoint(char *);

int main(void){
  char *str = "-4321";
  printf("String = %s, Converted to =  %d \n", str, strtoint(str));
}


int strtoint(char *instr){
  int j = 0;
  int mul = 1;
  int initValue = 0;
  int retValue = 0;

  if (instr[0] == '-'){
    mul = -1;
    initValue = 1;
  }

  for (j = initValue; j < strlen(instr); j++){
    retValue  *= 10;
    retValue += instr[j] - '0';
  }

  return mul*retValue;
}