Question

How to add leading zeros to the shorter string of two strings in C

Answer 1

#include <stdio.h>
#include <string.h>

void addLeadingZero(char* str1, char* str2) {
    size_t len1 = strlen(str1);
    size_t len2 = strlen(str2);

    char* str_to_pad = len1 > len2 ? str2 : str1;

    size_t diff = len1 > len2 ? (len1 - len2) : (len2 - len1);

    if (diff) {
        memmove(str_to_pad + diff, str_to_pad, len1 > len2 ? len2 + 1 : len1 + 1);
        memset(str_to_pad, '0', diff);
    }
}

int main(void)
{
    char str1[32] = "123";
    char str2[32] = "8976753";

    addLeadingZero(str1, str2);
    
    puts(str1);
    puts(str2);
}



/*
run:

0000123
8976753

*/

 

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Answer 2

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
 
char* addLeadingZero(const char* str1, const char* str2) {
    int len1 = strlen(str1);
    int len2 = strlen(str2);
 
    int diff = abs(len1 - len2);
 
    char* strToPad = (char*)malloc(sizeof(char) * (len1 > len2 ? len1 : len2) + diff + 1);
 
    if (diff > 0) {
        memset(strToPad, '0', diff);
        strcat(strToPad, len1 > len2 ? str2 : str1);
    }
 
    return strToPad;
}
 
int main() {
    const char* str1 = "123";
    const char* str2 = "8976753";
 
    char* result = addLeadingZero(str1, str2);
 
    printf("%s\n", str1);
    printf("%s\n", result);
    printf("%s\n", str2);
 
    free(result); 
 
    return 0;
}
 
 
 
/*
run:
 
123
0000123
8976753
 
*/

 

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Answer 3

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

char* addLeadingZero(const char* str1, const char* str2) {
    int len1 = strlen(str1);
    int len2 = strlen(str2);
 
    char* strToPad = (char*)malloc(sizeof(char) * (len1 > len2 ? len1 : len2) + 1);
    strcpy(strToPad, "");
 
    int diff = abs(len1 - len2);
 
    if (diff > 0) {
        memset(strToPad, '0', diff);
        if (len1 > len2) {
            strcat(strToPad, str2);
        }
        else {
            strcat(strToPad, str1);
        }
    }
 
    return strToPad;
}
 
int main(int argc, char *argv[]) {
    const char* str1 = "123";
    const char* str2 = "8976753";
 
    const char* result = addLeadingZero(str1, str2);
 
    printf("%s\n", str1);
    printf("%s\n", result);
    printf("%s\n", str2);
 
    return 0;
}
 
  
  
/*
run:
  
123
0000123
8976753
  
*/

 

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