C语言实现两个长整数相加

#include 
#include "string.h"
void addChar(char a[],char ch)//往字符串前加一个字符ch
{
    for(int i = (unsigned)strlen(a)+1; i>0; i--)
    {
        a[i] = a[i-1];
    }
    a[0] = ch;
}
int main(int argc, const char * argv[]) {
    char a[100],b[100],c[100];
    int len,lena,lenb,t=0,max;
    printf("请输入两个整数:");
    scanf("%s%s",a,b);
    lena = (unsigned)strlen(a);
    lenb = (unsigned)strlen(b);
    len = abs((lena-lenb));
    max = lena > lenb ? lena : lenb;
    for(int i = 0; i < len; i++)//将长度短的数前面补len个0
    {
        addChar((lena - lenb) > 0 ? b : a , '0');
    }
    for(int i = max-1; i >= 0; i--)//从后依次对应相加
    {
        int temp = a[i] + b[i] - 96 + t;
        c[i] = 48 + temp % 10;
        t = temp / 10;
    }
    c[max] = '\0';
    if(t)//如果第一位相加大于等于10则在前面补1
    {
        addChar(c, '1');
    }
    printf("\t%s\n",a);
    printf("  + %s\n",b);
    printf("  = %s\n",c);
    return 0;
}

• 结果如图
  
  

  这里写图片描述