atoi

atoi.c

#include <stdio.h>
#include <math.h>
#include <limits.h>

int myAtoi ( const char * str ){

int number = 0;
int index = 0;
int length;
int isNeg = 0;

for(length = 0; str[length]!='\0'; length++);

if(str[0] == '-'){
	isNeg = 1;
	index++;
	length--;
}

for(; length > 0; index++){

	if(str[index] >= '0' && str[index] <= '9'){
		number += (str[index] - '0')*pow(10,length-1);
		length--;
	}else{
		fprintf(stderr, "Error! Not a numerical. ");
		return -1;
	}
}

if(isNeg){
	number *= -1;
}

return number;
}

int main(){
    
char *testStr;

printf("%d\n",myAtoi("0021334"));
printf("%d\n",myAtoi("21334"));
printf("%d\n",myAtoi("-2334"));

printf("%d\n",myAtoi("-"));
printf("%d\n",myAtoi("0"));
printf("%d\n",myAtoi(""));

printf("%d\n",myAtoi("87p9"));
printf("%d\n",myAtoi("2-334"));

sprintf(testStr,"%d",INT_MAX);
printf("%s -> %d\n",testStr, myAtoi(testStr));
sprintf(testStr,"%ld",(long)INT_MAX+1);
printf("%s -> %d\n",testStr, myAtoi(testStr));

sprintf(testStr,"%d",INT_MIN);
printf("%s -> %d\n",testStr, myAtoi(testStr));
sprintf(testStr,"%ld",(long)INT_MIN-1);
printf("%s -> %d\n",testStr, myAtoi(testStr));

return 0;

}

output.txt

21334
21334
-2334
0
0
0
Error! Not a numerical. -1
Error! Not a numerical. -1
2147483647 -> 2147483647
2147483648 -> -2147483648
-2147483648 -> -2147483648
-2147483649 -> -2147483648