Put a number in array, and convert it from char to int

Question

Taking in input a number and then put every digit into an array, I have, converted it into a string so that I can put it into an array, but then when I use the cast to remake it a int i get the ascii number..

#include <stdio.h>
#include <stdlib.h>

int main(){

    char num_str[64] = {0};
    int num, cifra;

    printf("Write a number: \n");
    scanf("%d", &num);

    int len = snprintf(num_str, 64, "%d", num);
    printf("The length is %d\n", len);

    for(int i = 0; i < len; i++) {
        cifra = (int)(num_str[i]);
        printf("%d \n", cifra);
    }

    return 0;
}

Good, now how does one convert `'1'` into the integer 1? `(int)'1'` doesn't do the trick since it results in 49. — Micha Wiedenmann, Feb 13 '20 at 16:31
Does https://stackoverflow.com/questions/7021725/how-to-convert-a-string-to-integer-in-c help? — Micha Wiedenmann, Feb 13 '20 at 16:38
I need to convert a single char each time to a number not a string — awwww, Feb 13 '20 at 16:42
@awwww `cifra = ((int)(num_str[i])) - 48;` or `cifra = (int)(num_str[i]) - (int)'0';` although i'd rather use a dedicated function like `strtoi` to make it a lot more readable — John Doe, Feb 13 '20 at 16:46
also, what happens if someone doesn't write a number? like `A`? — John Doe, Feb 13 '20 at 16:48
@JohnSmith could you please show how it would be with strtoi? — awwww, Feb 13 '20 at 16:50
I'd read the number directly into the string. (If you were worried about validation, you'd be checking the return value from `scanf()` — which you should do anyway). You can then convert the digit characters into the corresponding number by subtracting `'0'` from the (ASCII) digits in the string: `if (scanf("%63s", num_str) == 1) { for (int i = 0; num_str[i] != '\0'; i++) { if (isdigit((unsigned char)num_str[i])) num_str[i] -= '0'; } }`. — Jonathan Leffler, Feb 13 '20 at 17:12

score 0 · Accepted Answer · answered Feb 13 '20 at 22:18

0

convert it from char to int

Test the character for digit and subtract '0'.

for(int i = 0; i < len; i++) {
    int cifra = num_str[i];
    if (cifra >= '0' && cifra <= '9') printf("%d\n", cifra - '0');
    else printf("%c\n", cifra);  // such as '-'
}

answered Feb 13 '20 at 22:18

chux - Reinstate Monica

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Put a number in array, and convert it from char to int

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