Convert String to Integer

Code

#include <stdio.h>
#include <stdint.h>

int custom_atoi(const char *str) {
    uint8_t i = 0;
    int result = 0;
    int sign = 1;

    // Skip leading non-digit characters except sign
    while (str[i] && (str[i] == ' ' || str[i] == '\t')) {
        i++;
    }

    if (str[i] == '-') {
        sign = -1;
        i++;
    } else if (str[i] == '+') {
        i++;
    }

    while (str[i] >= '0' && str[i] <= '9') {
        result = result * 10 + (str[i] - '0');
        i++;
    }

    return sign * result;
}

int main() {
    char str[101];
    fgets(str, sizeof(str), stdin);

    // Remove newline
    uint8_t i = 0;
    while (str[i]) {
        if (str[i] == '\n') {
            str[i] = '\0';
            break;
        }
        i++;
    }

    printf("%d", custom_atoi(str));
    return 0;
}

Solving Approach

1. Initialize i = 0, result = 0, sign = 1
2. Check for leading - or +
   • If str[i] == '-', set sign = -1, then increment i
   • If str[i] == '+', set sign = +1, then increment i
3. Loop through digits
   • While str[i] is between '0' and '9', build the number:

• result = result * 10 + (str[i] - '0')

• Increment i

  4.Return sign * result